# Fish Tanks with Potted Plants and No Filters



## dwalstad (Apr 14, 2006)

Last week, I posted my latest article 'Potted Plants for Fish Breeding Tanks' (10 pages, lots of pictures) on my website. Article has new data since 2017 and resulted from a recent talk I gave to Raleigh Aquarium Society.

None of the tanks have any filters or water circulation. Most have just a scattering of STS (Safety-Sorb clay gravel) on the bottom. All plants are mobile--potted, floating, or semi-attached. Tanks are for breeding fish, so all plants can be easily pulled out to catch fish. Attached are pictures of one tank and a table of water parameters that I measured (on August 8, 2021) for the 10 tanks. Interestingly, nitrates were almost zero except for one tank with 10 ppm. This despite the usual heavy feeding and infrequent water changes. Also, you'll note I have gone back to keeping LED lights on for 13 hours/day to maximize plant growth. No siestas. No time for plants to rest!


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## johnwesley0 (Feb 23, 2021)

Thank you for posting this. I read it as soon as I saw it referenced in one of the community threads and knew immediately that it deserved a thread of its own (but didn't want to get in front of you to do it.)

What can I say? What lovely tanks! What a lovely variety of sizes and shapes of jars and pots! IMHO, this is the future of the Walstad method because so many people have established tanks that have been cycled for years, who want to take the hobby to another level of naturalness but don't want to completely tear up their tanks in order to do so.

I also love how you have incorporated many of the issues discussed on these pages into one article, making the information even more accessible to the general public.


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## Garuda2520 (May 2, 2021)

Thank you for the article. Really interesting, especially since I just started a new tank couple of months ago with potted plants.

I'm interested how the 13 hour light period affected the tank in overall? Since I've been using the 5 hour - 4 hour siesta - 5 hour cycle.


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## johnwesley0 (Feb 23, 2021)

Biggest surprises:
1) That DW herself has only been filterless since 2019. This "confession" makes me feel as though we are all learning new things together (or, in "real time" as the kids like to say.)
and,
2) Her hypothesis that beneficial bacteria in the gravel (specifically, in Safe-T-Sorb, a kind of baked clay with industrial applications) could be a source of nitrate uptake. This is huge. It goes against years of indoctrination that nitrification is a one-way street.


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## ukamikazu (Jun 4, 2010)

@dwalstad when you mention that you're keeping your lights on for 13 hours straight, without continuously running a traditional bubbling sponge filter or just a soft gentle current from a small powerhead or some combination of these things you're not too concerned about possibly suffocating levels of carbon for the animal life nor a deficiency for the plant life? I presume you recommend rather light stocking levels?

I'm trying to see the balance here is what i'm getting at. For years we've used a siesta period to build carbon back up for the remainder of the photoperiod and run our aerators at night to avoid an oxygen crisis for the sake of the animals. What's the practical advice here, given this new data and lack of powered circulation?


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## jatcar95 (Oct 30, 2019)

ukamikazu said:


> @dwalstad when you mention that you're keeping your lights on for 13 hours straight, without continuously running a traditional bubbling sponge filter or just a soft gentle current from a small powerhead or some combination of these things you're not too concerned about possibly suffocating levels of carbon for the animal life nor a deficiency for the plant life? I presume you recommend rather light stocking levels?
> 
> I'm trying to see the balance here is what i'm getting at. For years we've used a siesta period to build carbon back up for the remainder of the photoperiod and run our aerators at night to avoid an oxygen crisis for the sake of the animals. What's the practical advice here, given this new data and lack of powered circulation?


Maybe I'm misunderstanding, but wouldn't running the lights for 13 hours straight add more oxygen to the water? Since the plants are photosynthesizing the entire time? As opposed to the siesta time, when they start consuming oxygen again.


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## jatcar95 (Oct 30, 2019)

dwalstad said:


> Last week, I posted my latest article 'Potted Plants for Fish Breeding Tanks' (10 pages, lots of pictures) on my website. Article has new data since 2017 and resulted from a recent talk I gave to Raleigh Aquarium Society.


@dwalstad just wanted to add my thanks for this article. Such a great resource to have on hand, lots of really concise information. I love my full-substrate Walstad, but now I'm really itching to set up a tank with potted plants!!


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## ukamikazu (Jun 4, 2010)

jatcar95 said:


> Maybe I'm misunderstanding, but wouldn't running the lights for 13 hours straight add more oxygen to the water? Since the plants are photosynthesizing the entire time? As opposed to the siesta time, when they start consuming oxygen again.


That's what I'm trying to wrap my mind around. I guess what I'm asking in my own confused way is
1. Are we relying solely on other processes like decomposition and animal respiration for the carbon during lights on and
2. What happens at night when there is no photosynthesis but neither is the water being disturbed to dissolve more O2? This is more an animal welfare question.

I'm also thinking the answer here is also dependent on stocking levels. Apologies if I wasn't clear. Such is the hazard of trying to follow up on your hobby and work from home at the same time .


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## mistergreen (Mar 3, 2007)

I have a small 5G filterless tank filled with crypts and endler-guppy hybrids. The tank definitely keeps the livestock in balance, in number and smaller size of the fish.


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## johnwesley0 (Feb 23, 2021)

From what I have been able to glean from dozens of posts on this subject, the two main points of a siesta schedule for lighting purposes, are that 1) a completely submerged aquatic plant pretty much uses up its ability to to uptake CO2 within the first four hours of daylight. That's because of the loss of a certain enzyme crucial in the photosynthesis process. The enzyme builds back up during the siesta period. So, it's not really as if you are gaining any more oxygen by leaving the lights on for 13 hours straight. The main benefit of the siesta period is

2) that it mitigates the growth of algae. Maybe, DW is less worried about algae in a potted aquarium?


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## ukamikazu (Jun 4, 2010)

Algae, I must admit, is a perennial concern of mine that the siesta period pretty much eliminated along with lots of healthy plant growth and not fertilizing the water column. I tell you, it's hard changing things up when you get used to doing things a certain way. I've always had at minimum a sponge filter with a powerhead and an airstone that comes on at night. They're almost protective charms for me at this point. Not very scientific, but there you are.


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## tiger15 (Apr 9, 2017)

I have a high tech tank in which all plants are mobile, either epiphytes on rock or potted. There is a thin layer of gravel barely cover up the bottom to eliminate reflection. I do it so I can easily move plants around to rescape without the mess of having to break up rooted plants in substrate. I use hydroponic net pots that allow roots to reach out and stay aerobic, and small rock for epiphytes so I can take them out to repot or re glue with no hassle. 

In my zero tech shrimp bowl with no water movement, plant mass is the sole source of oxygenation as surface gas exchange is mostly blocked by floaters. The bowl receives afternoon window sunlight and I can see O2 bubbling up like a fountain. Water testing showed that nitrate and phosphate are nearly non detectable at all time despite light feeding and regular partial water change with nutrient rich water from my high tech tank.


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## johnwesley0 (Feb 23, 2021)

My shipment of Safe T Sorb just arrived. There are no trucking supply stores near me in Brooklyn and the cheapest online supplier was about triple the deal they gave DW. That being said, and even with delivery costs - it was still in line with other gravel advertised for aquarium use but at about 10x the quantity!











I will probably not need this much gravel for the next 50 years, but I was really anxious to test out DW's theory about nitrate eating bacteria. If true, it would be a game changer for hobbyists who have already cycled their tanks and cannot stuff their tanks with enough fast growing plants to outcompete bacteria for ammonia and ammonium.

Safe T Sorb is a really interesting substrate in its own right. Coarser than potting soil but nor quite as chunky as ordinary gravel.









I was tempted (and still am) to take out all my pots and just lay down a thin layer on top of the mulm filled bottom of my porcelain bowl. But instead, I'm going to stick a container of it in a corner of the bowl and see what sort of parameters I get after a week or two. I rinsed out about two cups full and was pleased that, despite some bad reviews it received in another internet community ten years ago, it rinsed fairly easily and without a lot of residue.










Well, two cups turned out to equal about four inches of Safe T Sorb in my old cannister compartment and despite the fact that it contained no organic material, it seems granular enough that ways to mitigate the possibilities for it becoming _anaerobic _still seemed advisable. So I mixed about a dozen bio-filter media in with it. And, I sat it on top of another cannister compartment that would remain empty.


















Again, counter some advanced warnings, there was surprisingly little buoyancy when I placed the whole thing into my bowl (I did use the compartment cover to submerge it - but, took it off as soon as the contents were completely under water.)


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## dwalstad (Apr 14, 2006)

ukamikazu said:


> @dwalstad when you mention that you're keeping your lights on for 13 hours straight, without continuously running a traditional bubbling sponge filter or just a soft gentle current from a small powerhead or some combination of these things you're not too concerned about possibly suffocating levels of carbon for the animal life nor a deficiency for the plant life? I presume you recommend rather light stocking levels?
> 
> I'm trying to see the balance here is what i'm getting at. For years we've used a siesta period to build carbon back up for the remainder of the photoperiod and run our aerators at night to avoid an oxygen crisis for the sake of the animals. What's the practical advice here, given this new data and lack of powered circulation?





johnwesley0 said:


> From what I have been able to glean from dozens of posts on this subject, the two main points of a siesta schedule for lighting purposes, are that 1) a completely submerged aquatic plant pretty much uses up its ability to to uptake CO2 within the first four hours of daylight. That's because of the loss of a certain enzyme crucial in the photosynthesis process. The enzyme builds back up during the siesta period. So, it's not really as if you are gaining any more oxygen by leaving the lights on for 13 hours straight. The main benefit of the siesta period is
> 
> 2) that it mitigates the growth of algae. Maybe, DW is less worried about algae in a potted aquarium?


The accelerated plant growth takes care of the algae. The siesta builds up CO2 --not enzymes--for submerged plants, which need it in water. Floating plants can get it from air. I consider their good growth essential. (See 'Aerial Advantage' chapter in my book.)

Don't have computer at this time, so my answers will be brief and delayed until I get new one setup.


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## johnwesley0 (Feb 23, 2021)

Thanks, @dwalstad! I think you've given us a homework assignment until your new work station is set up. I've already started re-reading Ch. IX of EPA. 

EDIT: Yes, and there's also the piece in Ch.VI ("Carbon") that sums it up nicely:
*To compete, submerged plants have had to invest in costly photosynthetic equipment (enzymes) to capture CO2 when it is available. When CO2 is depleted, though, such as in the afternoon during intense photosynthesis, this equipment lies idle [skip] Plants must still maintain underused or idle equipment; this maintenance drains energy from the plant in the form of increased respiration. The result is reduced photosynthetic efficiency - and ultimately growth - of the freshwater plant.* (p.94)

So, yes. I either misread this the first time I sped through it or missed it entirely. The presence (critical mass) or absence of CO2 in the water is clearly the precipitating factor where submerged plants are concerned.

But, this still begs the question, why cease the siesta periods in your potted plant tanks? Is it because so many of them are potted _emergent_ plants?


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## dwalstad (Apr 14, 2006)

johnwesley0 said:


> Thanks, @dwalstad! I think you've given us a homework assignment until your new work station is set up. I've already started re-reading Ch. IX of EPA.
> 
> EDIT: Yes, and there's also the piece in Ch.VI ("Carbon") that sums it up nicely:
> *To compete, submerged plants have had to invest in costly photosynthetic equipment (enzymes) to capture CO2 when it is available. When CO2 is depleted, though, such as in the afternoon during intense photosynthesis, this equipment lies idle [skip] Plants must still maintain underused or idle equipment; this maintenance drains energy from the plant in the form of increased respiration. The result is reduced photosynthetic efficiency - and ultimately growth - of the freshwater plant.* (p.94)
> ...


You are an enthusiastic student!
I only stopped siesta because l wanted to look at my fish when l feed them at noon. I assume that it could make a difference for floating and emergent plants. Plants don't grow without light and these plants are not limited by CO2.


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## mistergreen (Mar 3, 2007)

I measured CO2 throughout the day on an NPT tank. The CO2 dropped a bit but there was still plenty of CO2. I think it was 15ppm down to 13ppm but rose up when the lights are off.


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## johnwesley0 (Feb 23, 2021)

mistergreen said:


> I measured CO2 throughout the day on an NPT tank. The CO2 dropped a bit but there was still plenty of CO2. I think it was 15ppm down to 13ppm but rose up when the lights are off.


But, would that not be the case when/if most of your plants are lucky bamboo, papyrus palms, and lotuses?


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## mistergreen (Mar 3, 2007)

johnwesley0 said:


> But, would that not be the case when/if most of your plants are lucky bamboo, papyrus palms, and lotuses?


They take CO2 straight from the air. Underwater, plants have a harder time getting CO2. It's so important, they (aquatic plants) change their leaves so it'll be easier to get CO2.


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## johnwesley0 (Feb 23, 2021)

mistergreen said:


> They take CO2 straight from the air. Underwater, plants have a harder time getting CO2. It's so important, they (aquatic plants) change their leaves so it'll be easier to get CO2.


Does that mean that with aerial leaves aquatic plants can produce more O2? If so, where does all that extra O2 go and does any of it wind up in the water column?


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## mistergreen (Mar 3, 2007)

johnwesley0 said:


> Does that mean that with aerial leaves aquatic plants can produce more O2?


Not sure about that. I doubt it.



johnwesley0 said:


> If so, where does all that extra O2 go and does any of it wind up in the water column?


O2 will diffuse into the water and any 'extra' will form bubbles that float out of the water (pearling).


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## dwalstad (Apr 14, 2006)

Emergent plants grow faster than submerged plants. They can clean up the water of nutrients (e.g., nitrates, ammonia, toxic metals, etc) faster than submerged plants. But floating plants add no O2 to water. It all goes into air. In fact, their leaves block oxygen diffusion from air into the water, so they can actually decrease the O2 in an ecosystem. That's why you need to have BOTH submerged and emergent plants. 

The pond folks know all about this. They always recommend oxygenating plants for ponds (e.g., submerged plants like Anacharis). 

Another thing I would say is that my tanks (5,10, and 20 gal) are only 12 inches high. This shallowness helps with oxygenation as there is a large surface area compared to water depth. As tank depth increases, there will be less oxygen entering the system from the air. Oxygen will affect bacterial activity and that can change water purification and many other things.


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## johnwesley0 (Feb 23, 2021)

Well, I know it's only been 5 days but I wasn't going to have another chance to measure my parameters for a while. Nevertheless, with only one or two top offs for the past month, my ammonia is still 0 ppm, nitrites 0 ppm and *nitrates somewhere between 5 and 10 ppm. Five days ago, the nitrates stood somewhere between 10 and 20 ppm. *Normal variation between test samples? Maybe. Put it this way, my parameters rarely improve without a partial water change and I haven't performed one in three weeks. I culled the floaters at the same time that I installed the Safe T Sorb, so it could be either one of them - or both acting in concert. Will check again in about a week.


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## johnwesley0 (Feb 23, 2021)

johnwesley0 said:


> Well, I know it's only been 5 days but I wasn't going to have another chance to measure my parameters for a while. Nevertheless, with only one or two top offs for the past month, my ammonia is still 0 ppm, nitrites 0 ppm and *nitrates somewhere between 5 and 10 ppm. Five days ago, the nitrates stood somewhere between 10 and 20 ppm. *Normal variation between test samples? Maybe. Put it this way, my parameters rarely improve without a partial water change and I haven't performed one in three weeks. I culled the floaters at the same time that I installed the Safe T Sorb, so it could be either one of them - or both acting in concert. Will check again in about a week.


So...it's been a week and I gotta say...I'm impressed. I just tested my parameters again: 0 ammonia/ammonium, 0 nitrites and this time there's no question, the nitrate level is firmly parked at 5ppm. That's nearly two weeks during which my nitrates have not increased and, to the contrary, have trended in the opposite direction. I have even attempted to "control" for the growth of my floaters:









As you can see, the _salvinia minima _is corralled behind plastic tubing and has had little room for growth the entire week, normally a recipe for rising nitrates in my bowl. My hypothesis, now a theory, is that *denitrifying bacteria *have taken up residence in my bowl and the most likely location are the unique surface crags and crevices presented by the STS introduced at the beginning of my observations.


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## dwalstad (Apr 14, 2006)

johnwesley0 said:


> My hypothesis, now a theory, is that *denitrifying bacteria *have taken up residence in my bowl and the most likely location are the unique surface crags and crevices presented by the STS introduced at the beginning of my observations.


I think you are right on!


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## dwalstad (Apr 14, 2006)

I was so encouraged by last month's measurements, that I monitored my ten tanks again yesterday. Note that I did not clean or change water in any tanks since the earlier measurements, except Tank # 1 (it got a thorough cleaning, plant pruning, and 50% water change).

The one tank without STS (#9) is definitely accumulating nitrates. Plants continue to do their job of removing nitrites and ammonia without filters, which is what I expected. But the removal of nitrates is totally new.


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## johnwesley0 (Feb 23, 2021)

It's been a month since my last water change and for the first time since I began posting on APC, I feel as though I might be able to join the "I only have to top-off" club.


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## dwalstad (Apr 14, 2006)

It's also the Mother Nature club.  

I value your input, because it has some thought (e.g., grasp of denitrification) AND you have read my book.

I am very excited about the nitrate results. I have long suspected that in a tank without CO2 injection, plants alone couldn't take up all the nitrogen.


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## johnwesley0 (Feb 23, 2021)

dwalstad said:


> It's also the Mother Nature club.
> 
> I value your input, because it has some thought (e.g., grasp of denitrification) AND you have read my book.
> 
> I am very excited about the nitrate results. I have long suspected that in a tank without CO2 injection, plants alone couldn't take up all the nitrogen.


THANK YOU. And, while I have you...About that #9 tank of yours. Is that a _stable _30ppms or do you periodically have to change the water? Just curious.

EDIT: Same question, but phrased slightly differently. Number 9 tank went from 10 ppm nitrates to 30 ppm nitrates in a month's time. Are the plants in that tank able to keep it within that range by themselves or do you have to intervene before things reach a dangerous level?


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## dwalstad (Apr 14, 2006)

Tank #9 was at 10 ppm nitrates a month ago. So it has gone from 10 to 30 ppm in one month. No water changes during this time.

I assume that plant growth and bacterial activity cannot keep up; nitrates will continue to accumulate. This tank is outside where temperatures are now getting cooler and there have been several rainy days without much light. That said, another tank (Tank #8) is outside and it shows low nitrates despite similar conditions. To make a definitive statement I would have to 3 tanks with STS and 3 tanks without, all in the house.

Nitrates alone are not toxic, but if I can, I prefer that they do not accumulate. I am thrilled with results for the other 9 tanks. In the past, my tanks with full substrates usually had 10-40 ppm nitrates. 

Today, I cleaned out Tank #9 and did a 70% water change. I am so pleased that I may reset up this tank in the house with STS!


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## johnwesley0 (Feb 23, 2021)

I guess this is one of those "the proof is in the pudding" moments:









Now, if that's not 0 nitrates, I don't know what is!
This has been a very interesting last couple of hours because in attempting to answer another question on the "Suitable soils for the Walstad tank" thread, I wound up doing a deep dive on STS only to discover that the stuff has been around for ages. People have always been attracted to its natural, river bed color - and the fact that it is dirt cheap (no pun intended.) It's amusing to read from the benefit of 20/20 hindsight that everyone's initial desire was to use it as a straight substrate. I think because it looked so natural like soil that they had to be disabused of the notion that it contains any nutrients at all. People also wanted to use it as a cap only to discover that it was lighter and airier than gravel and held plants down only with difficulty.

Only one post mentioned STS in connection with the denitrification process and that was only because of its resemblance to Oil Dri, another tractor supply substance that was being touted as the main medium in a so-called, "anoxic filtration system". But, that's a subject for another thread. What's remarkable here is that STS seems to be creating the conditions for anaerobic bacteria to thrive without actually being anaerobic, at least not in ways that are familiar to any of us on APC.
EDIT: familiar to us who work with dirted tanks.
EDIT: Perhaps, it's not a biological process at all, but a chemical one?


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## dwalstad (Apr 14, 2006)

Wow! Talk about confirmation!

I think that you have put two and two together. I agree that STS alone is a poor substrate and as a soil cover okay, but not the best. Oil Dri is in same category as STS--baked clay.

For the potted plant tank, though, STS and Oil Dri might be perfect! They have clay dust and porous crevices for bacterial attachment and colonization. Associated nitrifying bacteria, as they use oxygen, create the MILDLY anaerobic conditions for denitrification even in environments that don't seem anaerobic to us.

Others viewing my results have questioned whether the STS is taking up N directly. I don't think so. First nitrates are negatively charged, so they do not bind to soil particles. Second, plants prefer ammonia, so they aren't going to take up nitrates unless they absolutely have to. I know of no chemical reaction that would convert ammonia to nitrates. I believe what we are witness here is biological process. 

Third, any ammonia binding to soil particles is a one-shot process. The NH4+ cation would have to compete with other cations for a limited number of negative binding sites on clay particles (my book, p. 126, Fig VIII-3). In contrast, nitrate respiration is a continuous on-going process. It never stops. Just as we use oxygen for our respiration, these bacteria are continuously drawing down on nitrates for their respiration.

I didn't think a scattering on the glass would make that much difference, but maybe it can. 

I cleaned up and brought Tank #9 with 30 ppm nitrates inside where it will have lighting and temperature similar to a "Twin Tank," #7. My concern was that plants in #9 didn't have maximum growth because the lighting and temperature outside were not as favorable as indoors. Attached is picture of two tanks. I tried to make tanks as similar as possible-same water, lighting, fish load, etc. The only big difference is that there is no STS in #9. Starting nitrates for both tanks was zero on 9/12. Stay tuned!


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## dwalstad (Apr 14, 2006)

Preliminary results to report! I've measured no nitrates in Tanks #7 and #9 at 3 weeks. The nitrates that accumulated in Tank #9 while it was outdoors may have resulted from reduced plant growth due to lower temperatures (65F many days) and lower light levels than the indoor tanks. (I've taken PAR readings for shaded sunlight and it is MUCH less than overhead LED or CFL intensity.)

Still, the STS may have had an effect. My preliminary results don't really test it adequately. 

Thus, I have ordered some pure KNO3 and NaNO3. What I can do is add enough of the KNO3 to each tank to produce 20 ppm nitrates in each tank. Then, I can monitor the two tanks to see if the STS actually makes any difference in nitrate levels. 

Will nitrates go down faster in Tank #7? Will they go down at all? If results look interesting, I might repeat the comparison with NaNO3. 

I ordered the two pure chemicals from HomeScience for a total cost of only $17.25. This will provide me with some cheap entertainment over the holidays!


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## johnwesley0 (Feb 23, 2021)

This is a wonderful venture on your part, sure to be of interest no matter the results. One technical question, since it's been a while since I've taken a science course: Technically speaking, which tank would be considered the "control"? The one w/o or the one with the STS?


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## dwalstad (Apr 14, 2006)

I don't think it matters here that much. Since I'm testing for the effect of STS, it could be that Tank #7 with the STS is the experimental tank and Tank #9 (without STS) is the control. 

Here's some more food for thought: 

Planned study with KNO3 additions is to figure out why my tanks don't accumulate nitrates. One possibility is that robust plant growth takes up the ammonia--preferred N source of aquatic plants-- faster than any nitrifying bacteria can convert it to nitrates. So I'm not sure that plants remove nitrates; they just prevent them from being generated in the first place. (In my tanks without filters, this is a possibility.) If I do see nitrate removal, it could be via denitrification. In that case, the STS layer in Tank #7 could make a difference, possibly by encouraging denitrification.


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## johnwesley0 (Feb 23, 2021)

dwalstad said:


> One possibility is that robust plant growth takes up the ammonia--preferred N source of aquatic plants-- faster than any nitrifying bacteria can convert it to nitrates.


I wish I had a dollar for every time I've read this: "My NPT has successfully cycled, but I don't understand why my plants don't seem to be growing."


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## dwalstad (Apr 14, 2006)

Reporting unpredicted end of my STS experiment. Presence of STS bottom layer didn't seem to affect 10 ppm added nitrates. But within two days, 4 out of 36 guppies died in Tank #9 without the STS. Emergency! Measured 0.5 ppm ammonia in this tank. Thus, I abruptly ended the experiment by changing 75% of water and adding enough STS (6 cups) to cover bottom of Tank #9. My take: STS not only binds ammonium but provides attachment sites for bacteria that decrease ammonia levels. Thus, while plants purify the water, STS gives me an extra level of protection. Now, I have STS in all of my tanks. None have filters and last week I disconnected all bubbling from air pumps. Photo shows today's picture of Tanks #7 and #9 after stopping the experiment the day before. Water in #9 is a little cloudy due to clay particles, but that's fine. And if you use STS, please do not discriminate against clay cloudiness and rinse STS until the water runs clear. Clay has a HUGE surface area to bind ammonium and provide attachment sites for bacteria. Thus, I only rinse STS once before adding directly to the tank. Clay cloudiness is good!


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## johnwesley0 (Feb 23, 2021)

So, what was going on with the spike in ammonia? Does something similar to DAP (p.66 EPA) occur? In that section, you described a reaction whereby certain bacteria convert nitrates into ammonium. I suppose one could imagine a situation where there is an excess of nitrates that triggers a similar reaction that results in higher ammonia?


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## dwalstad (Apr 14, 2006)

It would be impossible to sort out all the variables to make a definitive statement. I doubt the ammonia spike was due to DAP, because DAP is associated with fermentation and very anaerobic sediments. 

Time will tell on this one. My goal is to continue to raise and breed guppies in these potted tanks without filters, pumps, and mechanical aeration. Tanks will depend on plant growth with STS as a backup.


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## johnwesley0 (Feb 23, 2021)

dwalstad said:


> It would be impossible to sort out all the variables to make a definitive statement. I doubt the ammonia spike was due to DAP, because DAP is associated with fermentation and very anaerobic sediments.
> 
> Time will tell on this one. My goal is to continue to raise and breed guppies in these potted tanks without filters, pumps, and mechanical aeration. Tanks will depend on plant growth with STS as a backup.


It was a noble effort. Each one of your guppies deserves a posthumous medal!


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## dwalstad (Apr 14, 2006)

Just posted a revision of my Potted Plant article on my website. 

In order to revise my Potted Plant Tank article, I tested the effect of an STS gravel layer on the potential removal of added nitrates. I added 10 ppm nitrates to a 20 gal tank with STS (Safe-T-Sorb) and 10 ppm nitrates to a matching 20 gal tank without STS. Goal was to see whether denitrification or nitrification explained the nitrate accumulation I had observed earlier in one of the 10 tanks described in my article. Over a period of 13 days, I measured absolutely no decrease in nitrates in either expt tank. Attached is file describing the expt testing STS's effect on the added nitrates. 

Unexpectedly, I ran into a "lurking variable." The guppies in the expt tank without STS were from an older batch that I believe was genetically less "fit" than the batch in the expt tank with STS. Guppy fitness/age may have explained the deaths that occurred during expt, not absence of STS.


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## johnwesley0 (Feb 23, 2021)

Ah, but did the expt tank without STS register a spike in ammonia as happened in your previous nitrate dosage? That was the baffling part (IMO). it was almost as if something was reverse engineering the extra nitrate back into ammonia?

Wait. I guess I should read the article first. 

EDIT: Never mind. DeadFish= increase in NO3. 

Fascinating. So, we're still left with the puzzle of STS somehow increasing nitrification without - seemingly - to increase nitrates. Possible explanations being that plants are perfectly capable of increasing their uptake of nitrates? Potted plants?


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## dwalstad (Apr 14, 2006)

Please read the article. The subject is complicated and has many variables and blind alleys. Dead fish may have been due to genetic weakness, certainly not nitrates. Nitrates are not toxic. (For a better experiment, I should have used randomly selected individuals in both tanks drawn from one guppy population.) STS is a minor variable that may be irrelevant. However, I believe STS or any baked clay type gravel may be useful, because of clay's known greater nutrient and bacterial binding capacity than sand or gravel or no substrate.

The main take-home message is that good plant growth in 9 out of my 10 tanks removed toxic forms of nitrogen- ammonia and nitrite. I now believe--based on my experiment--that the nitrate accumulation in the outdoor tank was due to nitrification, not denitrification Overall, the article trumpets "Plant Power."


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## johnwesley0 (Feb 23, 2021)

dwalstad said:


> The main take-home message is that good plant growth in 9 out of my 10 tanks removed toxic forms of nitrogen- ammonia and nitrite. I now believe--based on my experiment--that the nitrate accumulation in the outdoor tank was due to nitrification, not denitrification Overall, the article trumpets "Plant Power."


Oops. I just realized i should have said "DeadFish=increase in NH3"
Be that as it may, 
i still applaud you for the effort. It's made STS a tad less mysterious and reinforced the primacy of biological processes that are already familiar to hobbyists. For me the take-home message was: every tank is different.


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## Michael (Jul 20, 2010)

Diana, thanks so much for this!


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## jake37 (Mar 18, 2021)

I'm sorry but what is STS ? I really can't keep track of all these abbreviations.


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## johnwesley0 (Feb 23, 2021)

jake37 said:


> I'm sorry but what is STS ? I really can't keep track of all these abbreviations.


STS= Safe-T-Sorb

To quote from an earlier post:


> People have always been attracted to its natural, river bed color - and the fact that it is dirt cheap (no pun intended.) It's amusing to read from the benefit of 20/20 hindsight that everyone's initial desire was to use it as a straight substrate. I think because it looked so natural like soil that they had to be disabused of the notion that it contains any nutrients at all. People also wanted to use it as a cap only to discover that it was lighter and airier than gravel and held plants down only with difficulty.
> 
> Only one post mentioned STS in connection with the denitrification process and that was only because of its resemblance to Oil Dri, another tractor supply substance that was being touted as the main medium in a so-called, "anoxic filtration system". But, that's a subject for another thread. What's remarkable here is that STS seems to be creating the conditions for anaerobic bacteria to thrive without actually being anaerobic, at least not in ways that are familiar to any of us who work with dirted tanks.


Some of us theorized that STS might have been initiating some sort of ionization process in the water like some of the commercially available products already on the market, but @dwalstad eliminated that as a possibility fairly early in her speculations.


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## Michael (Jul 20, 2010)

jake37 said:


> I'm sorry but what is STS ? I really can't keep track of all these abbreviations.


I feel your pain! Let me remind everyone to spell out any abbreviation at least once in a discussion or post.


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## dwalstad (Apr 14, 2006)

STS, because of its porosity and clay component and high surface area, has plenty of binding sites for nutrients (CEC or 'cation exchange capacity'). It also has plenty of attachment sites for bacteria. If the STS is anaerobic, say at bottom of a deep substrate filled with organic matter, it will support denitrification, an anaerobic process. On the other hand, if the same STS is in an aerobic environment with enough oxygen, it will support aerobic bacteria like nitrifying bacteria. It simply provides attachment sites for bacteria, and since it also binds nutrients (NH4+, K+, etc), it encourages bacterial activity.

Apparently, the thin layer of STS scattered on the bottom of my potted plant tanks stays aerobic, and thus, does not support denitrification. I wasn't sure about this until I did my experiment showing that 10 ppm added nitrates did not decrease over a 13 day period. If tanks were actively denitrifying, I should have measured some decrease in nitrates.

I bought a 40 lb bag of STS for $7 at Tractor Supply Co.


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## johnwesley0 (Feb 23, 2021)

dwalstad said:


> STS, because of its porosity and clay component and high surface area, has plenty of binding sites for nutrients (CEC or 'cation exchange capacity'). It also has plenty of attachment sites for bacteria. If the STS is anaerobic, say at bottom of a deep substrate filled with organic matter, it will support denitrification, an anaerobic process. On the other hand, if the same STS is in an aerobic environment with enough oxygen, it will support aerobic bacteria like nitrifying bacteria. It simply provides attachment sites for bacteria, and since it also binds nutrients (NH4+, K+, etc), it encourages bacterial activity.
> 
> Apparently, the thin layer of STS scattered on the bottom of my potted plant tanks stays aerobic, and thus, does not support denitrification. I wasn't sure about this until I did my experiment showing that 10 ppm added nitrates did not decrease over a 13 day period. If tanks were actively denitrifying, I should have measured some decrease in nitrates.
> 
> I bought a 40 lb bag of STS for $7 at Tractor Supply Co.


So, it's still conceivable that someone (not saying who necessarily) could concoct the right anaerobic conditions for denitrifying bacteria to thrive by say, stacking a couple of old filter containers filled with STS on top of each other and just letting them sit at the bottom of their tank?


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## jake37 (Mar 18, 2021)

dwalstad said:


> STS, because of its porosity and clay component and high surface area, has plenty of binding sites for nutrients (CEC or 'cation exchange capacity'). It also has plenty of attachment sites for bacteria. If the STS is anaerobic, say at bottom of a deep substrate filled with organic matter, it will support denitrification, an anaerobic process. On the other hand, if the same STS is in an aerobic environment with enough oxygen, it will support aerobic bacteria like nitrifying bacteria. It simply provides attachment sites for bacteria, and since it also binds nutrients (NH4+, K+, etc), it encourages bacterial activity.
> 
> Apparently, the thin layer of STS scattered on the bottom of my potted plant tanks stays aerobic, and thus, does not support denitrification. I wasn't sure about this until I did my experiment showing that 10 ppm added nitrates did not decrease over a 13 day period. If tanks were actively denitrifying, I should have measured some decrease in nitrates.
> 
> I bought a 40 lb bag of STS for $7 at Tractor Supply Co.


So STS is a geo specific product ? I mean it is more of a brand's name for a product but specific to that brand that may not be available in other geolocation. You describe its behavior but if i were to go to the store it would be next to impossible for me to determine if an alternative product had the right properties ?

Having said this - i have some interest in the topic since I have found that a specific fine inert substrate rapidly produce anaerobic pockets but there is a difference between that type of anaerobic pocket and what you are describing since i find it rapidly kill plants (I've run the experiment several times) - I suspect the difference between this substrate and STS is the clay component allowing for porous property and therefore the anaerobic bacteria you are describing is a bit different. I have another substrate (also inert) that does not have this 'kill plant' property which i have described as porous.

In the first case i am describing above i had a heavily stocked aquarium that I did not perform water changes for 3 months (because it was on the floor and siphoning water out was difficult) but the nitrate level stayed below 2. This was an inert substrate - but instead of releasing sulfur (egg smell) i applied a gentle current over it and it release (I think) nitrogen and very small patches of cyobo developed on it - the positive effect of this gentle current was that the plants grew instead of dying.


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## johnwesley0 (Feb 23, 2021)

jake37 said:


> So STS is a geo specific product ? I mean it is more of a brand's name for a product but specific to that brand that may not be available in other geolocation. You describe its behavior but if i were to go to the store it would be next to impossible for me to determine if an alternative product had the right properties ?


It's hard to believe there aren't other baked clay products out there with similar properties but under different brand names. It's intended use was (as the brand name implies) for soaking up oil spills in busy truck and long-haul vehicle destinations. Surely, other countries around the world have trucks and surely someone has figured out a way to soak up oil with industrialized clay.

After following @dwalstad's research, my attitude towards STS has changed slightly. I used to think of it as performing some sort of alchemy within the water. But, now I think of it as a kind of super-efficient bio-ring, perhaps 100x more commodious to beneficial bacteria (BB) than anything else aimed at the aquarium market. Based on my own experience - and with the proviso that "every tank is different" - I think you could get away with having a bag of the stuff sitting at the bottom of your aquarium; maybe a more solid container, like a small clay pot, if you are really trying to create anaerobic conditions?


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## Michael (Jul 20, 2010)

Safe-T-Sorb is calcined (fired or baked) montmorillonite clay:








Montmorillonite - Wikipedia







en.wikipedia.org





As mentioned in the article, it is also used as a soil amendment and an ingredient in bonsai soil mix. I use it as an aquarium substrate and in bonsai mix with great results. I've never used it as Diana describes (thin layer over the bottom glass) but most of my tanks have it as a cap over soil. And if I am using a high organic matter or very fertile "soil", I mix the soil half and half with STS. One such tank has been running for over 10 years.

I have been raising platies for a few years, and they are next to impossible to catch in a normal planted tank! The next tank I set up will be potted plants and a thin layer of STS. Thanks again, Diana.


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## dwalstad (Apr 14, 2006)

STS (Safe-T-Sorb) is a natural clay (montmorillonite of the smectite clay group) mined in western Tennessee (USA). The company's nearby plant heats the clay to 800 degrees F which produces a calcined clay (clay hardened via melting). That temperature results in a material that is _partially_ ceramic. As such it is very absorbent and effective in soaking up liquids, which is its intended purpose. SEACHEM heats their clay from northern Georgia to a higher temperature (1,200 F) from which they get FLUORITE. (Reference: Neil Frank, noted planted tank expert.)

For making pottery, clay is fired/heated to 1,000 to 2,500F. The high temperature melts and hardens the clay particles, somewhat like heating sand to create glass. The clay becomes a ceramic, the hardness depending on the firing temperature.

Kitty litter is only heated to dehydrate (get rid of absorbed water). Dehydration can be done at much lower temperatures (250F? or 150C). Thus, kitty litter has no structure and rapidly breaks down into fine particles (i.e., mud). Mixed with an organic potting soil, kitty litter mud would be highly reactive--release aluminum to create aluminum toxicity?-- whereas any aluminum release from STS gravel would be much more gradual and controlled, such that plant roots could handle it. 

Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity. In addition, tropical clays may contain iron oxides and aluminum oxides deposited inbetween clay particles. These oxide deposit can cause even more metal toxicity problems. In my book (p. 132) I describe a tank meltdown experience I had from mixing potting soil with just a little bit of laterite clay. It created iron toxicity.

Michael here describes mixing STS with soil. Another knowledgeable hobbyist reported getting good results potting plants in a mixture of STS and soil. STS has a good reputation from experienced hobbyists, including our very own Michael!


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## johnwesley0 (Feb 23, 2021)

*Seachem* ($35 for a 15lb. bag) gets a lot of mentions on this forum. Has anyone ever tried using it as a bio-filter; perhaps, even as an _anaerobic _bio-filter_?_


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## mistergreen (Mar 3, 2007)

johnwesley0 said:


> *Seachem* ($35 for a 15lb. bag) gets a lot of mentions on this forum. Has anyone ever tried using it as a bio-filter; perhaps, even as an _anaerobic _bio-filter_?_


I've read people putting it in a porous container in a low flow area of the sump for an anaerobic filter. It needs iron to work so an iron-rich material would work.


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## johnwesley0 (Feb 23, 2021)

mistergreen said:


> I've read people putting it in a porous container in a low flow area of the sump for an anaerobic filter. It needs iron to work so an iron-rich material would work.


It's interesting to read the chatter that has accompanied _denitrification _at various stages of the hobby over the years. If you google Seachem and anaerobic, you see references to Matrix(TM) a volcanic pumice derivative sold at about $16 a pound. It was touted as a more efficient successor to "live rocks" which were actual rocks mined from the ocean floor and popular among saltwater tank enthusiasts for their ability to support colonies of beneficial bacteria. A few years later, the company introduced Denitrate(TM) another gravel-like substance which Seachem straight up touted as being similar to Matrix, (so, Is there much difference between volcanic pumice and calcined clay?) And, judging from the comments on their Amazon pages, users were convinced they had to replace the products every few months as if they were charcoal and would lose their "power" eventually. Curiously, neither product is particularly popular as far as aquarium products go, barely breaking the top 200 "aquarium filter accessories" category in Amazon's Best Seller's Rank.


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## jake37 (Mar 18, 2021)

My biggest concern in this thread is introducing toxicity to the tank. When I read the above past about clay contain aluminium or iron it just makes me thing I should stick to inert substrate. The plants might not grow as well but they grow and the fishes don't have to worry about long term poisoning. 

I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ?


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## johnwesley0 (Feb 23, 2021)

jake37 said:


> I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ?


Calcined clay is similar to porcelain and people have been keeping fish in porcelain bowls for a thousand years. I can't speak for the chemical properties of Matrix and Denitrate except to say that Seachem advertises them both as being "inert".


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## mistergreen (Mar 3, 2007)

johnwesley0 said:


> It's interesting to read the chatter that has accompanied _denitrification _at various stages of the hobby over the years. If you google Seachem and anaerobic, you see references to Matrix(TM) a volcanic pumice derivative sold at about $16 a pound. It was touted as a more efficient successor to "live rocks" which were actual rocks mined from the ocean floor and popular among saltwater tank enthusiasts for their ability to support colonies of beneficial bacteria. A few years later, the company introduced Denitrate(TM) another gravel-like substance which Seachem straight up touted as being similar to Matrix, (so, Is there much difference between volcanic pumice and calcined clay?) And, judging from the comments on their Amazon pages, users were convinced they had to replace the products every few months as if they were charcoal and would lose their "power" eventually. Curiously, neither product is particularly popular as far as aquarium products go, barely breaking the top 200 "aquarium filter accessories" category in Amazon's Best Seller's Rank.


I bet we can buy pumice or even perlite and put them in mesh bags, it would be a lot cheaper. Their pores are bigger than the baked red clay but they don't have the iron needed in the denitrification process. The pores do eventually get clogged up with biomatter but that's simply solved by baking or bleaching the organics away. Maybe a mix of pumice and baked red clay would work best. Since we're in the plant hobby, we need nitrogen for the plants so we don't need this setup.


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## johnwesley0 (Feb 23, 2021)

mistergreen said:


> the iron needed in the denitrification


Is that because iron binds oxygen?


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## jake37 (Mar 18, 2021)

I'm not disagreeing or agreeing but the post above mine by Diane has:

"Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity."

which seems inconsistent with your statement or perhaps i am misunderstanding something...



johnwesley0 said:


> Calcined clay is similar to porcelain and people have been keeping fish in porcelain bowls for a thousand years. I can't speak for the chemical properties of Matrix and Denitrate except to say that Seachem advertises them both as being "inert".


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## mistergreen (Mar 3, 2007)

johnwesley0 said:


> Is that because iron binds oxygen?


I think the anaerobic denitrifiers use iron and carbon to convert NO3 => N2


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## johnwesley0 (Feb 23, 2021)

jake37 said:


> I'm not disagreeing or agreeing but the post above mine by Diane has:
> 
> "Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity."
> 
> which seems inconsistent with your statement or perhaps i am misunderstanding something...


I'm not contradicting @dwalstad. I'm quoting her. Or, at least _paraphrasing _her:


dwalstad said:


> For making pottery, clay is fired/heated to 1,000 to 2,500F. The high temperature melts and hardens the clay particles, somewhat like heating sand to create glass. The clay becomes a ceramic, the hardness depending on the firing temperature.


A few of the pots used for her "potted plants" are made of clay. I'm assuming the baking process affects a chemical change of some sort upon the iron.


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## dwalstad (Apr 14, 2006)

_My biggest concern in this thread is introducing toxicity to the tank. When I read the above past about clay contain aluminium or iron it just makes me thing I should stick to inert substrate. The plants might not grow as well but they grow and the fishes don't have to worry about long term poisoning.

I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ? _

In nature, fish are found in lakes with clay sediments and rivers filled with turbidity from clay particles. Neutral pH and oxygen in aquariums and most natural waters neutralize aluminum and iron toxicity. (Iron and aluminum oxides are not toxic to fish, plants, or humans.) Plant roots in anaerobic substrates are the vulnerable ones, not fish.


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## johnwesley0 (Feb 23, 2021)

dwalstad said:


> _My biggest concern in this thread is introducing toxicity to the tank. When I read the above past about clay contain aluminium or iron it just makes me thing I should stick to inert substrate. The plants might not grow as well but they grow and the fishes don't have to worry about long term poisoning.
> 
> I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ? _
> 
> In nature, fish are found in lakes with clay sediments and rivers filled with turbidity from clay particles. Neutral pH and oxygen in aquariums and most natural waters neutralize aluminum and iron toxicity. (Iron and aluminum oxides are not toxic to fish, plants, or humans.) Plant roots in anaerobic substrates are the vulnerable ones, not fish.


Thank you for this explanation, Diana. I have page 132 permanently bookmarked in my copy of _Ecology of the Planted Aquarium _(EPA) and, for whatever reason, it is only clear to me now that you were writing about toxicity to plants, not fish. D'Oh!


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## dwalstad (Apr 14, 2006)

_I'm assuming the baking process affects a chemical change of some sort upon the iron. _
Yes. High heat changes the chemical bonds so that the atoms no longer react. It does not change the atomic composition.


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## dwalstad (Apr 14, 2006)

_Thank you for this explanation, Diana. I have page 132 permanently bookmarked in my copy of Ecology of the Planted Aquarium (EPA) and, for whatever reason, it is only clear to me now that you were writing about toxicity to plants, not fish._

If I revise book, I will try to make this more clear. It is certainly an important point, so thanks for bringing it to my attention!


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## FernKing (4 mo ago)

dwalstad said:


> STS (Safe-T-Sorb) is a natural clay (montmorillonite of the smectite clay group) mined in western Tennessee (USA). The company's nearby plant heats the clay to 800 degrees F which produces a calcined clay (clay hardened via melting). That temperature results in a material that is _partially_ ceramic. As such it is very absorbent and effective in soaking up liquids, which is its intended purpose. SEACHEM heats their clay from northern Georgia to a higher temperature (1,200 F) from which they get FLUORITE. (Reference: Neil Frank, noted planted tank expert.)
> 
> For making pottery, clay is fired/heated to 1,000 to 2,500F. The high temperature melts and hardens the clay particles, somewhat like heating sand to create glass. The clay becomes a ceramic, the hardness depending on the firing temperature.
> 
> ...


I am a ceramics artist and here is a useful chart on what happens to clay materials (both chemically & physically) when they are fired. It may give you some insight on why STS behaves differently than kitty litter besides the varying chemical makeup. STS appears to be fired just before “quartz inversion” and/or _some _quartz inversion may be happening.


https://ceramicartsnetwork.org/docs/default-source/uploadedfiles/wp-content/uploads/2013/02/kilnfiringchart.pdf


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## FernKing (4 mo ago)

dwalstad said:


> Just posted a revision of my Potted Plant article on my website.
> 
> In order to revise my Potted Plant Tank article, I tested the effect of an STS gravel layer on the potential removal of added nitrates. I added 10 ppm nitrates to a 20 gal tank with STS (Safe-T-Sorb) and 10 ppm nitrates to a matching 20 gal tank without STS. Goal was to see whether denitrification or nitrification explained the nitrate accumulation I had observed earlier in one of the 10 tanks described in my article. Over a period of 13 days, I measured absolutely no decrease in nitrates in either expt tank. Attached is file describing the expt testing STS's effect on the added nitrates.
> 
> Unexpectedly, I ran into a "lurking variable." The guppies in the expt tank without STS were from an older batch that I believe was genetically less "fit" than the batch in the expt tank with STS. Guppy fitness/age may have explained the deaths that occurred during expt, not absence of STS.


I’ve been thinking about this. Did you use “new” STS straight from the bag? Maybe the STS needs to be “seasoned” by sitting in an aquarium for a while to acquire nitrogen fixing bacteria? Maybe STS straight out of the bag has no bacteria?


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## dwalstad (Apr 14, 2006)

The STS had been in the aquarium for awhile. You're right that straight out of the bag--after being baked at 1,000+F--it would have no relevant bacteria. 
However, I consider the STS irrelevant in my tanks. The plants are taking up the ammonia so fast that it never gets converted to nitrates. 
In tanks without heavy plant growth, STS could have a beneficial effect.


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## FernKing (4 mo ago)

dwalstad said:


> The STS had been in the aquarium for awhile. You're right that straight out of the bag--after being baked at 1,000+F--it would have no relevant bacteria.
> However, I consider the STS irrelevant in my tanks. The plants are taking up the ammonia so fast that it never gets converted to nitrates.
> In tanks without heavy plant growth, STS could have a beneficial effect.


Okay that sounds like a good goal to shoot for. Eliminate the ammonia before it has a chance for mischief 👍


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