# Safe T Sorb Clay for NPTs?



## dwalstad (Apr 14, 2006)

Dirt Lovers! I obtained some useful info on STS (Safe T Sorb) during a Nano Tank aquascaping demonstration by the noted aquarist Mark Denaro (author of _The 101 Best Freshwater Nano Species_). Demo was sponsored by the Raleigh Aquarium Society (RAS).

Mr. Denaro used STS as the substrate (2 Photos). Attractive product, inexpensive, and used for years by Aquatic Gardeners Association. 40 lb bags sell at Tractor Supply stores for about $7. Apparently, STS works well for large High Tech tanks with artificial CO2 injection and fertilizers.

For an NPT, I would not substitute it 100% for soil; it doesn't have any organic matter or major nutrients to get plants off to a good start in a new setup.

HOWEVER, STS might make an excellent cover/cap for a soil substrate. I've always used gravel or sand, but I think that STS might be better. Here's why. Unlike gravel, it will "capture and bind" nutrients released by the soil substrate in a new setup. The release of excess nutrients into the water is often a problem with fertile soil substrates. Fresh STS would act like a nutrient sponge in a new setup. Long term, the STS along with the soil, would serve as a reservoir of nutrients for rooted plants.

STS is special. It is a montmorillonite clay heated to about 800F. This moderate heating partially solidifies the natural clay particles, changing them to a firmer, more glass-like material. Clay is converted to pottery, usually with much higher temperatures (~1800F?), while kitty litter is heated (300 F?) only to dry out the clay. Apparently, the STS breaks down a little over time but nothing like kitty litter, which eventually forms a gummy mess.

For a comparison of gravel versus STS as a soil cap, I set up two 2 gal tanks with an organic potting soil underlayer. I capped the soil in one tank with gravel as usual; the other with STS. I planted _Sagittaria graminea_ and _S. subulata_ in each and changed water twice in both tanks (Photo). The next day, the STS tank's water still had some turbidity, but most was gone the next day.

On the third day (Photo), the gravel cap tank had orange/brown-tinted water, which is pretty typical. (An organic soil often releases humic acids.) What was amazing, though, is that the STS tank did not show this tinted water! My soil textbook describes the absorption of humic acids by clay particles.

On fourth day, I changed the water and both tanks looked decent (Photo)

Also, the pH was neutral in the STS tank and high (~8.2) in the gravel tank. This reflects the STS absorption of bicarbonates, which could bring down the KH. (STS is known to sometimes reduce the KH.)

I measured and found no ammonia in either tank. (I may have to repeat experiment using a more fertilized soil.)

I think the STS cap would counteract the occasional, temporary release of excess nutrients and humic acids from some soils. Plus it looks nice and is inexpensive!


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## Michael (Jul 20, 2010)

I love this stuff and use it as a cap in almost all my tanks. Also, if the soil substrate is highly organic (as is the case with most commercial potting mixes) I mix STS half and half with the potting mix for all the reasons that make it a good cap.


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## dwalstad (Apr 14, 2006)

With your experience and valued opinion, I'm now really fired up. 

Thanks, Michael!


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## dwalstad (Apr 14, 2006)

Racoons got into the tanks two days ago and ended my experiment. Alas, I took photo today of the aftermath and after removing some plants. It shows the greater tea-color from humus in the tank with gravel (tank on right). Note how the tank on the left with STS has much less humus color.

Clay is negatively charged and so is humus. They should repel each other. How then does clay bind humus? The answer is “cation bridges.” My soil textbook* shows the binding of humus to clay via cation bridges. That is, clay binds cations shown in the figure as metals (Al+++, Fe+++, Ca++, Mg++, etc); humus in turn binds to the cations. Sometimes, this binding includes water, as shown in Fig 18.6b. The textbook makes a point that Na+, with only one positive charge, will NOT serve as cation bridge.

* Wild, Alan. 1988. Russell's Soil Conditions and Plant Growth (11th Edition). John Wiley & Sons (NY), 991 pp. Figure is from p. 582.


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## Rodgie (Dec 28, 2017)

This is really an amazing new proven informations. I recently set up a walstad bowl, even with just kitty litter mixed with my potting soil, I can right away see the advantage of having clay. Not too much of those tannin colors. And I think I’m getting very less algae this way compared to my previous set up without clay.


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## Michael (Jul 20, 2010)

I hate raccoons!


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## dwalstad (Apr 14, 2006)

Rodgie said:


> This is really an amazing new proven informations. I recently set up a walstad bowl, even with just kitty litter mixed with my potting soil, I can right away see the advantage of having clay. Not too much of those tannin colors. And I think I'm getting very less algae this way compared to my previous set up without clay.


Very interesting and thank you for writing. I honestly had not realized the value of clay, in whatever its forms. I may add a small revision in next printing (#12) of my book about this! Granted, I've been a little slow to pick up on this. It was only the STS results--very stunning-- that sent me back to my soil textbook.

BTW, the STS used for the August RAS (Raleigh Aquarium Society) demo was provided by Neil Frank, previous editor of 'The Aquatic Gardener'. Neil is now using STS in his tanks. It was his idea for Mark Denaro to use the STS for his aquascaping demo.


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## Rodgie (Dec 28, 2017)

Thank you Ms. Diana. I wouldn’t be confident to set up my bowl without Sir Michaels help. Clay mixed with the soil is so far showing me really better results. Though knowing that the cat litter will turn into a mud. I put the clay first as first layer (tiny amount) then soil on top, and lastly the 2-3mm natural gravels. I’m sure cat litter mud would suffocate the soil over time if i put it above the soil. 

By any chance you’re gonna come up with a new revised book about ecology of planted aquarium Ms. Diana?


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## dwalstad (Apr 14, 2006)

Rodgie said:


> Thank you Ms. Diana. I wouldn't be confident to set up my bowl without Sir Michaels help. Clay mixed with the soil is so far showing me really better results. Though knowing that the cat litter will turn into a mud. I put the clay first as first layer (tiny amount) then soil on top, and lastly the 2-3mm natural gravels. I'm sure cat litter mud would suffocate the soil over time if i put it above the soil.
> 
> By any chance you're gonna come up with a new revised book about ecology of planted aquarium Ms. Diana?


You seem pretty savy on this kitty litter business, such as not putting it on top of soil. I plan to try a few experiments with kitty litter and STS. It seems I was too fast to condemn clay in general based on dismal results with a commercial clay product (Dupla's laterite).

I don't plan to prepare a revised edition of _Ecology of the Planted Aquarium_ until or unless it needs to be revised. I don't see that much has changed. A new edition would be mostly cosmetic and to slap on a newer publication date so that book doesn't look "dated."

For the clay-humus binding business, what I'll probably do--as I've done in the past--, is add "replacement pages" with the next printing. I will make sure that the eBook gets updated as well.


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## dwalstad (Apr 14, 2006)

I was getting ready to tear down the two experimental tanks when I realized that it would be easier just to reset the tanks up and "soldier on." I will continue to follow tanks for next precious weeks of summer to see if there is any effect of STS on plant growth.

More importantly, I realized that I was falling into the beginner trap of expecting only perfection with no setup problems.

Thus, I removed most of water yesterday, replanted with _S. graminea, S. subulata_, and a sprig of _H. difformis _(submersed form). Yes, the soil was disturbed and lying on surface, but so what? (If the tank ends up like Mysiak's, it won't matter.) I added small stones to hold plants down and a 1/4 cup more of soil covering. Then, I changed water twice.

Photo shows tanks after their new makeover. Tanks will now get enhanced night-time security!


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## dwalstad (Apr 14, 2006)

I have some interesting results from my bottle jar experiments that have made me think twice--and thrice-- about recommending STS. Unexpected results!

This bottle test experiment was designed to show that an STS cap would capture ammonia in the water and the soil. So I soaked the STS/soil in a liquid fertilizer solution containing 15 ppm ammonia for a few minutes. Then, I changed water to remove the ammonia for my start on 8/22 (Photo). Two days later on 8/24, I measured notably less NH3 in jars with STS, just like I had hoped and predicted.

However, at about 12 days, the NH3 increased dramatically in STS jars to 5 ppm. The two sand jars showed no ammonia. I think the STS acidity created a "soil meltdown." Dying soil bacteria and other microbes released their ammonia into the water.

Granted, my bottle tests don't reflect the tank situation where there's more oxygen and a greater volume of water over the STS. Some people treat the STS beforehand with baking soda. Probably not a bad idea. I have a feeling that neutralizing the acidity of the STS beforehand would have prevented the soil meltdown, but that's another experiment. 

Attached are pictures of the bottles and my measurements of the water.

Bottom Line: Be careful using STS as a soil cover!! Gravel and sand are safer, less complicated.


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## hoppycalif (Apr 7, 2005)

Thanks for the head's up! I was just planning on a trip to buy some STS at Tractor Supply, about 2 blocks from me. I may decide to go back to either pool filter sand or Black Beauty blasting grit. (My tank is down now, waiting for a move in a couple of months, and restarting the tank)


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## Michael (Jul 20, 2010)

Since my tap water is hard and highly buffered to a pH of 7.8, I think changes due to STS are beneficial.


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## dwalstad (Apr 14, 2006)

My tapwater is moderately hard. GH = 9 and KH = 7. My concern is that people with softwater may cover soil with an inch or more of STS, totally oblivious to the fact that a large volume of STS will generate acidity. With experienced aquarists like yourself, STS presents no problem and can be advantageous.

That said, I still have 2 more experiments, ones that deal with plant growth. Will post the results within next month. 

Also, I've started scattering small amounts of STS to create a thin layer in a guppy breeding tank with potted plants. Will monitor pH, but I think the STS will work just fine, better than the bare glass bottom that I previously had.

Until my stash of cheap STS runs out, I'll continue to play with it.


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## hoppycalif (Apr 7, 2005)

dwalstad said:


> My tapwater is moderately hard. GH = 9 and KH = 7. My concern is that people with softwater may cover soil with an inch or more of STS, totally oblivious to the fact that a large volume of STS will generate acidity. With experienced aquarists like yourself, STS presents no problem and can be advantageous.
> 
> That said, I still have 2 more experiments, ones that deal with plant growth. Will post the results within next month.
> 
> ...


My last set-up cost me $55 for substrate. This one will be less than $20. El Natural is also El Cheapo!!


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## Michael (Jul 20, 2010)

Por favor, El Barato!


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## Am2020 (Sep 10, 2019)

For those interested in using safe-T-sorb. Use clarifier and fine filter floss when first starting the tank up. This stuff has a lot of dust and will take several days to clear up and about a week to reach near perfect clarity if using a large canister filter. As soon as you disturb it there will be a cloud of fine silt released. Only takes a few hours to clear up after replanting a few things. STS is also very light and difficult to plant stem plants at first. There's a lot of air trapped inside each piece of substrate and will take a few weeks to remove all of it. After a year or two, it all becomes very soft and easy to break into mud with the slightest pinch. Will need to be replaced yearly for the average person that likes to plant and rearrange things.

I suggest 1/2" to 1" of topsoil with osmocote fertilizer mixed in. Then cover with fiberglass screen material. Several rocks along the outer edges of the screen to hold it down. Then cap it with 2" to 4" of STS. The screen material prevents the topsoil from breaking out when a plant is uprooted. Allows plants to be disturbed more often without releasing too much nutrients into the water column and cause an algae outbreak. I also use a thin layer of heavier planting substrate to cap the STS. Makes it easier to plant stem plants or any buoyant pearling plants from floating up. After a few months the STS becomes heavier and easier to plant into.


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## hoppycalif (Apr 7, 2005)

Am2020 said:


> For those interested in using safe-T-sorb. Use clarifier and fine filter floss when first starting the tank up. This stuff has a lot of dust and will take several days to clear up and about a week to reach near perfect clarity if using a large canister filter. As soon as you disturb it there will be a cloud of fine silt released. Only takes a few hours to clear up after replanting a few things. STS is also very light and difficult to plant stem plants at first. There's a lot of air trapped inside each piece of substrate and will take a few weeks to remove all of it. After a year or two, it all becomes very soft and easy to break into mud with the slightest pinch. Will need to be replaced yearly for the average person that likes to plant and rearrange things.
> 
> I suggest 1/2" to 1" of topsoil with osmocote fertilizer mixed in. Then cover with fiberglass screen material. Several rocks along the outer edges of the screen to hold it down. Then cap it with 2" to 4" of STS. The screen material prevents the topsoil from breaking out when a plant is uprooted. Allows plants to be disturbed more often without releasing too much nutrients into the water column and cause an algae outbreak. I also use a thin layer of heavier planting substrate to cap the STS. Makes it easier to plant stem plants or any buoyant pearling plants from floating up. After a few months the STS becomes heavier and easier to plant into.


Welcome to APC! Those are interesting suggestions. I always wash the dust out of substrate material like this. I would much rather do that than suffer the dust in the tank. And, the screen on top of the soil can result in a real mess if the roots of a plant get woven into the mesh, and you try to pull it up to replant it.


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## Michael (Jul 20, 2010)

Two inches of STS is acceptable, but four inches is too much. That depth puts you at risk of anaerobic substrate.


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## Am2020 (Sep 10, 2019)

hoppycalif said:


> Welcome to APC! Those are interesting suggestions. I always wash the dust out of substrate material like this. I would much rather do that than suffer the dust in the tank. And, the screen on top of the soil can result in a real mess if the roots of a plant get woven into the mesh, and you try to pull it up to replant it.


The roots will get stuck in the screen and will need to be cut with a knife. Most of my plants are carpeting plants with shallow roots. I have a few swords in the corners and just use my thumbnail to break the roots from the screen.

STS is so light that it doesn't trap any significant amount of gasses from the anaerobic areas. I find that I don't have any toxic hydrogen sulfide build up. Even with the organic top soil that has lots of wood pieces and plant material that will decompose. The substrate size is also big enough to allow plenty of flow to the lower layers. It's not like sand. The plant roots also help transport oxygen deep into the substrate. I keep the front short and slope it high towards the back. I've seen people use lava rocks or bricks to build height in the back and never heard of any issues with hydrogen sulphide gas problems. I feel like that's a myth and a scapegoat for other problems that occur.


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## dwalstad (Apr 14, 2006)

Am2020 said:


> Then cap it with 2" to 4" of STS.


How do you address any possible problems with acidity? I can't imagine a 2-4" layer of STS not generating some acidity. Do you treat the STS with anything beforehand? Add baking soda to the water, etc?


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## Seattle_Aquarist (Mar 7, 2008)

Hi @dwalstad,


I added two handfuls of STS to a quart jar of tap water ([email protected] after 24 hours to de-gas) and found minimal drop in pH over a 2 week period. Possibly I should check that again?


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## Am2020 (Sep 10, 2019)

dwalstad said:


> How do you address any possible problems with acidity? I can't imagine a 2-4" layer of STS not generating some acidity. Do you treat the STS with anything beforehand? Add baking soda to the water, etc?


I'm doing EI fertilizer method and the weekly 50% water changes keep the pH above 6.5

The CO2 is cranked up pretty high right now because it's a dense jungle but will cut back after the next heavy trimming. I try to keep the pH at 6.4 to 6.5 range because some the plants seem to do better at that range.

Regarding ammonia release. I believe it would take a much thicker layer of STS to prevent ammonia from the soil breaking through into the water column. A thin layer of sand can easily create a tight seal and prevent the ammonia from escaping if not disturbed by burrowing livestock. But STS is so porous and doesn't compact enough to create a tight seal. I don't know how well it absorbs ammonia compared to zeolite but I've never had any issues when using 2" to 4" cap.


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## Am2020 (Sep 10, 2019)

Seattle_Aquarist said:


> Hi @dwalstad,
> 
> I added two handfuls of STS to a quart jar of tap water ([email protected] after 24 hours to de-gas) and found minimal drop in pH over a 2 week period. Possibly I should check that again?


Just a theory, but I think STS is capable of growing a lot more bacteria than most substrates. Maybe the bacteria is producing a lot of CO2 and causing the water to soften and lower pH.

Next time you see a drop in pH. Take out some water into a wide bowl and let it sit out for a day. Then see if the pH rises or stays the same. If my theory is correct the pH should shoot up after gassing off the CO2

If the pH is dropping from a chemical reaction like a barley baile in a pond. Then shouldn't it happen immediately?


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## dwalstad (Apr 14, 2006)

Am2020 said:


> Regarding ammonia release. I believe it would take a much thicker layer of STS to prevent ammonia from the soil breaking through into the water column. A thin layer of sand can easily create a tight seal and prevent the ammonia from escaping if not disturbed by burrowing livestock. But STS is so porous and doesn't compact enough to create a tight seal. I don't know how well it absorbs ammonia compared to zeolite but I've never had any issues when using 2" to 4" cap.


Thanks for answer, but I was talking about acidity (i.e, low pH), not ammonia (NH3). I assume that you just washed your STS and put it into the tank. And that you did not soak it with anything beforehand.


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## Am2020 (Sep 10, 2019)

Here's my 55 when I started it up. Has 5 lbs of red clay mud on bottom. Then 1" - 2" layer of top soil from homedepot, cheapest bag they sold. Screen mesh layer and then capped with STS. For a total of 3" in the front and 4.5" in the back. Set up in August 3, 2019.


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## Am2020 (Sep 10, 2019)

August 3, 2019

















August 4, 2019

















Close up of the different layers. I prefer to see the layers than having a solid layer look.









August 6, 2019. Water sprite growing like a weed. Everyday I see a noticable amount of growth.









My first tank with STS was a 20L and it was a nightmare with algae growth. I think the cap was too thin only an inch thick. Every time I moved a plant, there were chunks of soil and wood chips floating around and releasing too much nutrients into the water column. Later did a 265 with just STS and never had any issues but wasn't happy with growth rates due to not dosing fertz or CO2. Did several glass jar tests with dirt and liked the results so much that i decided to do a 55 high tech EI method. The 55 has a layer of window screen material between the topsoil and STS to help keep the soil from escaping.


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## zolteeC (Dec 26, 2017)

Am2020 said:


> I'm doing EI fertilizer method and the weekly 50% water changes keep the pH above 6.5


I like the look of this STS cap (as long as it does not degrade over time), but there is no way for me to do 50% water changes weekly in my tank(s). That is not fun with 500+ liter water, I don't want to become a slave of my aquariums.

Anyways, the look of the tank above can be perfectly achieved with regular no co2 dirt + cap, for example look at @mysiak 's jungle.

Does this STS cover work better with sensitive carpeting plants under non CO2 dosing conditions? What is the potential benefit?


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## Am2020 (Sep 10, 2019)

zolteeC said:


> Anyways, the look of the tank above can be perfectly achieved with regular no co2 dirt + cap, for example look at @mysiak 's jungle.


A dirted tank with organics decomposing underneath will release a significant amount of CO2. So injecting CO2 is not a must but helps. After testing out photo rest periods with my lights. I'm a firm believer that the rest periods help build up more CO2 for the next photo period to use up.



zolteeC said:


> Does this STS cover work better with sensitive carpeting plants under non CO2 dosing conditions? What is the potential benefit?


I've never had a dirted tank for more than two years without replacing the soil. So it doesn't bother me that after a year the STS begins to crumble apart. At around two years the pieces all become smooth and rounded. Especially if you have MTS or cories pushing them around. The STS becomes so soft that a light pinch will smoosh a piece flat like wet clay.

The hardest part about using STS is trying to keep large stem plants with no roots from floating up. Every time my water sprite would begin to pearl, it would float up. Had to hold it down with drift wood or small stones until it rooted. Plants can actually root very easily in STS. For small carpeting plants I use a tiny drop of superglue gel to glue them to a heavier pieces of gravel before planting. Helps keep the cories from uprooting. I would recommend trying the dry start method first when using STS. Let the carpeting plants grow some roots first before adding fish. When you first use STS it has a lit of air trapped inside each piece. Poking around will only release the pockets of air between the pieces but not the air inside of them. Doesn't take long for them to become water logged. So don't worry if you struggle to keep stems from floating up. Let the tank cycle and by then you shouldn't have much trouble.

BTW...STS is my favorite looking substrate I've found. Love the variations in size, shape , and especially color. Really reminds me of the streams and springs I grew up with near my home. Just seems very natural and doesn't distract from the colors of the fish and plants. Most substrates I've used are either too uniformed in shape and size, or too black or red for my ttaste. This also doesn't have nearly as much dust as Seachem's red flourite plant substrate. That stuff turned my tank orange for a week.


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## Michael (Jul 20, 2010)

This has been an interesting discussion. All of my tanks are Walstad tanks, and most are set up with STS. I've tried other cap materials (fluorite, blasting grit, pea gravel, expanded shale) and STS remains my favorite. The only rival is the dark gray Turface that they don't make anymore. I like STS for both aesthetic and functional reasons.

STS will begin to break down over the years, but this hasn't been a problem for me. The fine particles from the break-down migrate downward, leaving the large particles on the top. And if the substrate isn't too deep, you can freshen the cap by washing some more STS and spreading a thin layer.

As Am2020 points out, fresh STS is very fluffy and buoyant. This can make planting and replanting a new tank a little difficult. But after a year or so, STS becomes firmer and more compact. I think this is when anaerobic substrate from excessive depth can become a problem. Of course, by this point the rapid decomposition of organ matter has slowed, reducing the risk.

Moving plants in established STS tanks has not been difficult for me, but I don't tend to rearrange things very often. When I do, I go slowly. Plants with strong root systems are lifted to expose just enough roots to anchor them in their new location. Then I cut the rest of the roots and leave them in the substrate. This can still make a cloudy mess, but a large water change and lots of mechanical media in the filter takes care of it.

Just as a side note, I only use mechanical media in my filters now. The filter is mostly for circulation and secondarily for removal of particles. I rely on plants and bacteria in the tank for other filtration.


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## dwalstad (Apr 14, 2006)

Am thoroughly enjoying the recent posts! Encouraging. 

Just for fun, I soaked STS in tapwater overnight and got a HUGE increase in GH. KH was zero. pH declined to 6 or below. 

I'm thinking now that the STS carries with it some calcium and/or magnesium. (In my bottle test results-- posted in this thread earlier--I couldn't tell whether the big GH increase was coming from the STS or the soil.)

STS might be good soil cover for people with softwater that want to increase their GH?


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## dwalstad (Apr 14, 2006)

My results using STS in planted bowls gave much different (and better) results than those in the pint jar tests. In bowls, I didn't see much difference between using sand or STS as a soil cover. [I added a bit (~3/4 cup) of sand to the STS bowl to help hold plants down.] The KH, pH, and GH were about the same, plus no ammonia (see results). Plants are growing just fine in both bowls. In fact, I plan to keep them both going and add some RCS (Red Cherry Shrimp).

I'll probably be using STS in my tanks, since it's so inexpensive and Sir Michael has had good results long-term with it. Folks trying it out for the first time might want to monitor the KH and the pH for first few weeks. In hardwater situations, the KH lowering might be advantageous, plus one can always add baking soda if KH and pH gets too low.

I have been recommending organic potting soils, but this might be too restrictive. The potting soil I used for the bowls was not organic and it is working well. It has a low NPK (0.023, 0.03, 0.06), but it contains chemical fertilizers (ammonium phosphate, ammonium nitrate, potassium nitrate, potassium sulfate, calcium phosphate). The chemicals are polymer-coated to be released slowly. I wasn't sure this was true, but it seems to be the case.

Photos show test results, setup of bowls, then bowls at 2 days and 26 days. The bowl on the right is the one with the STS/sand cover.

Factors that would explain the different results between bowls and jar results are:


The ratio of STS to water was 1:16 in bowls, but only 1:3 in jars. [Jars contained ½ cup of STS and 1.5 cups water compared to 1 cup STS in the 1 gal (16 cups) bowl.]

In jars, the STS depth was 1.5 inches (too deep!); in bowls about 0.5 inches. The jar's thicker STS layer would make the soil more anaerobic. Also, in bowls, the substrate had a greater surface area, and thus, increased exposure to oxygenated water.

In jars, I started with a much more fertile potting soil (NPK= 1.1%, 0.3%, and 0.35%). Moreover, I added a dilute liquid fertilizer (1/2 cup containing 15 ppm ammonia) to the potting soil (1/2 cup) in each jar. In contrast for the bowls, I used a different potting soil (2 cups/bowl) that had a much lower NPK (0.023%, 0.03%, 0.06%), and I did not add any fertilizer to it.

The presence of plants would oxygenate the water and root area.


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