# Rejuvenating Old Substrates



## dwalstad (Apr 14, 2006)

An APC member TammyWhyNot wrote this in another thread and I didn't want to see it buried before a little "airing out." It's a very unusual approach to rejuvenating old substrates. She suggested adding an inch layer of sand to stimulate stalled plant growth in old tanks with decreasing plant growth. In her words:

_ "I've been experimenting for years. I'm also a HUGE fan of yours and have 2 copies of your book and several of your articles. I also have friends with salt water tanks who've suggested that deeper substrates (at least in marine tanks) are actually beneficial because they have both aerobic and anaerobic layers to them. The anaerobic layers are good at breaking down nitrates. So I tried it on one of my Walstad tanks that had been set up for 6 years that was starting to lose nutrients and gain algae and within a week, the nuisance algae disappeared and plant growth (particularly my Cryptocorynes) started to rejuvenate. I've had it this way now for over 2 years and it is stable. Same inch of organic soil plus inch of gravel cap I started out with just an additional inch of sand." 

"Perhaps the trumpet snails and established root system help with the gas and nutrient exchange but not for certain. Another thing I've noticed is with my older soil tanks, after about several years I would have to add a few root tabs for the heavy feeders but the ones I've capped with sand, I haven't had to add any additional nutrients to. I've read that some anaerobic conditions can make nutrients more readily available to plants so that could be the case plus I never gravel-vac anymore just let the detritus break down for the invertebrates. But these are my experiences. Before I read your book, I couldn't keep fake plants alive but now I'm giving plant cuttings away left and right. You're definitely the template I go by every time I set up a tank but I still like to color outside of the box and try additional approaches now and again."_

It could be that in older tanks (more than a year old) the substrate goes so aerobic that nutrients become less available. (In terrestrial systems, plant nutrients are most available under mildly anaerobic conditions.) In aquatic systems its hard to imagine a sediment going too aerobic. However, I would not dismiss an experienced hobbyist's long-term experience. Under certain conditions (lots of trumpet snails, thoroughly decomposed organic matter, massive root growth), maybe, just maybe adding a sand layer and making the substrate more anaerobic could rejuvenate an old substrate.

Food for thought....


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## florida phish fan (Dec 3, 2020)

Thanks for this thread Miss D. Your book was the gateway drug into the NPT. I stumbled across an article, then bought the book, wondered if I could pull it off... and was hooked....

I have a question about "refreshing" vs "re-setting". 

I've been procrastinating about "refreshing" two year old ADA Aquasoil (I didn't have the guts to start with potting soil). I'm pretty sure it's spent because for one thing the PH has gone up (it was below 7 for the longest time) and some root feeders aren't looking too good (10g understocked, so I've been messing around with ferts). I don't want to add more fish until I get the soil sorted. 

I have some Amazonia in storage but I'm not up for washing it separately for a month until it stops leaching ammonia. 

According to some, this tank should be re-set - as in completely new soil. I'm up for that - but I'd use potting soil this time. The 2 yr old spider wood definitely needs to go, so I'm thinking time for a new look. 

However, I'm wondering if I should just "re-fresh" instead of replacing soil? 
If so, any suggestions? I was thinking of mixing some Controsoil into it, but the ADA seems to be disintegrating. Lots of particulates if disturbed - all that can't be mulm. (I vacuum lightly). It's a pain. 

I'm reluctant to use root tabs because the soil isn't really deep enough (rooky mistake, didn't anticipate how much it would settle). 

Thank you much in advance for your time. Of course, all responses are appreciated 







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## dwalstad (Apr 14, 2006)

florida phish fan said:


> I have a question about "refreshing" vs "re-setting".
> 
> I've been procrastinating about "refreshing" two year old ADA Aquasoil (I didn't have the guts to start with potting soil). I'm pretty sure it's spent because for one thing the PH has gone up (it was below 7 for the longest time) and some root feeders aren't looking too good (10g understocked, so I've been messing around with ferts). I don't want to add more fish until I get the soil sorted.
> 
> ...


Before tearing down a tank, I would consider the sand idea. Since your tank doesn't have a deep substrate, this might help. I would stop vacuuming the substrate. You're just removing plant nutrients.

I've had really good results fertilizing my potted plant with an water soluble fertilizer made by Miracle Gro. It has an NPK of 15:30:15. Lots of P and less N, which is good. (Its composition is designed to induce flowering.) What I do is pull pot of tank, let water drain out and then squirt in a little fertilizer solution. Let that drain a little and then put pot back in the tank.

You could modify what I'm doing. I would remove the fish and all the water. Tilt tank so that the water drains and collects at one end. Remove the water, such that you now have a damp substrate and no water on top. Then squirt in some liquid fertilizer. If you do this right, the ADA should have enough CEC to grab onto the nutrients. Remember that the fertilizer should not be too dilute. The more concentrated it is, the more it will replace cations already attached to soil particles. See my book, p. 126. All you are doing is exchanging ions. In an established tank, you should have enough nitrifying bacteria in the soil and enough plant growth to take care of ammonia and nitrites. 

If the ADA is disintegrating, that's good. The smaller the particles, the more surface area for bacteria and the more CEC to hold nutrients. Don't remove those fine soil particles, probably clay. Give them a few hours to settle out of the water.

What I've suggested is for advanced hobbyists that like to experiment and don't want to tear down an established tank. I've never done it, but I think it would work.

Good luck!


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## dwalstad (Apr 14, 2006)

This is the Miracle Gro Bloom Booster fertilizer I use. You can get a life-time supply (1.5 lb) about anywhere for around $8. To make my fertilizer stock solution, I mixed a teaspoon (~7 grams) of the blue crystals with 500 ml of water. Doesn't have to be exact! I have fertilized a few pots now and haven't had any problems so far. I'll be using this solution to rejuvenate my old pots and feed my houseplants.


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## florida phish fan (Dec 3, 2020)

Thank you much for the detailed reply!

This tank is a bit of a saga. I didn't vacuum for a long time; finally it got too gross. Now I have to pour water through a collendar, otherwise the tank turns into a snow globe. So... I've been lightly vacuuming esp a couple of low flow areas. 

Interesting idea about the sand/ferts. I'm thinking as long as I have to go through the trouble of catching fish and uprooting plants ( some are over crowded) AND replace the wood (it's too rotted) might as well have some fun and go for a new look. 

Couple questions?

#1 that fertilizer trick - just let it soak in, then pour sand over existing dirt? How long will that last? 
Something I've wondered about sand - wouldn't it prevent the soil/water interactions I'm assuming are happening? Also, there's a thin layer of scattered river rock type gravel, and fish that like to graze are always picking at it (as do tiny fry). 

#2. Can you dose with that fertilizer as you would other ferts? If I don't fertilize I wind up with dying plants and an algea farm.. 

I'd LOVE to try a tank with potted plants. Sounds like a fun winter project. 

p.s. there's a filter on this tank housing some cheap sponge material and presumably loads of bacteria - haven't had an ammonia reading since it was cycled. That ammonia leaching soil made it easy, and the plants thrived until the magic wore off. Then I couldn't get a nitrate reading (ever) without ferts. Hungry plants....

Thanks for your insight and handy tricks. 



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## dwalstad (Apr 14, 2006)

I think you just have to do what suits you best. From your post, it sounds like you have a grip on the situation. 

Good luck!


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## florida phish fan (Dec 3, 2020)

Thank you. More like starting to get a feel - hardly a grip . 

Very curious to know if you use the liquid MG in your tanks with fish? 



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## dwalstad (Apr 14, 2006)

Yes. But I am cautious. At any one time (every 2 weeks or month), I might fertilize 1 or 2 pots per tank with about 5 ml per pot. I pull pot out, let it sit on newspaper to drain out some of water, then dribble the blue fertilizer solution over the drained soil. Before adding pot back to the soil, I let the pot sit a few minutes so fertilizer can drain into soil.

I was a little worried that this might cause problems, but I haven't seen any. Fish and shrimp fine. No big algae blooms, plants just growing better. I suspect that any fertilizer not absorbed by soil particles is too little to harm anything and/or plants must be taking it up from the water. I will know more after I do monthly measurements of all 9 tanks next week.

Of course, for rejuvenating an entire tank substrate, you would be adding much more fertilizer than 5-10 ml. I assume that anyone trying it would measure ammonia and nitrite after adding water back to the tank and before adding the fish. Again, if these are well-established tanks, the eco-system should be strong enough to process a goodly amount of fertilizer.

I'm still working this out with my potted plants. Please understand that I could be wrong. But I have about 50 potted plants now and the idea of repotting 50 plants is as intimidating as setting up a new tank! In the past, we've had people suggest rejuvenating old substrates by inserting frozen cubes of soil. My liquid fertilizer method COULD be easier, because you are not disturbing plant root systems nor freezing cubes of soil.


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## florida phish fan (Dec 3, 2020)

Thank you for the detailed reply. I'm taking notes in my hardcopy notebook (not a Luddite, phone is too distracting). 

50 plants to repot? Egads, I might hire some neighborhood kids as "assistants".  

I've been thinking about your sand solution, and may just do that. Some plants are crowded and need to be moved. I like that Carib Sea Peace River gravel - perhaps I could incorporate some of that.
I've only had dirted tanks since I forayed into planted tanks. 

I'm wondering how long the MG would last before the process has to be repeated again? 

Also, there's dwarf sagittaria in the tank. Ok to uproot it and replant in the sand? Will the plants remain healthy until the roots make it down to the dirt? 

There's a couple small swords with long root systems. Should I trim the roots before replanting? Logistically, I can't just dump 2" of sand on top of them. 

If this is a bit discombobulated apologies - had a pipe burst at 2 a.m. and pulled an all nighter. I'm a bit baked. 

Good luck with those plants! Photos? 🪴




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## kamlesh barot (Jun 7, 2014)

I use empty capsules and fill them with organic slow release fert







, approved by the vendor. Sow them deeply in my old Amazonia substrate, every week after 50% water is removed, but before adding new tap water. The plants have bounced back & BBA has vanished.


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## dwalstad (Apr 14, 2006)

florida phish fan said:


> I'm wondering how long the MG would last before the process has to be repeated again?
> 
> _Let the plant growth tell you and/or if algae starts becoming a problem (due to reduced plant growth)._
> 
> ...


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## florida phish fan (Dec 3, 2020)

Thank you Diana. I didn't mean to sound so heavy handed (as in dumping 2" of sand) LoL. 
An inch is fine and gently lifting the small swords is a fine idea. 

I'm wondering if I should let these tiny Ember tetra fry grow up a bit first? They like to pick at whatever's in the soil. Covering it with sand would deprive them of whatever it is they're eating. They prefer it over powdered fry food. 

Burning Question! I remember reading about your unfortunate experience with bacteria invasion in your tanks and how helpful it is to run a UV light. 
I have one ready to go. 
I've always wondered if the light would kill off infusoria or whatever microbes fry eat? 

Thanks and Cheers! 

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## florida phish fan (Dec 3, 2020)

Beautiful set up! Plants look so healthy. I wonder tho - why the need to use ferts every week?
Your plants don't look like the type that need a lot of ferts. Doesn't it raise Nitrates into the red zone? 

Sounds like your using homemade tabs like osmocote? I thought you put those in every few months? Under heavy root feeders? 

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## dwalstad (Apr 14, 2006)

_Burning Question! I remember reading about your unfortunate experience with bacteria invasion in your tanks and how helpful it is to run a UV light. I have one ready to go.
I've always wondered if the light would kill off infusoria or whatever microbes fry eat? _



UV light kills bacteria suspended in the water. It would not hurt the substrate or a filter ecosystem where the bacteria are living attached. I would only use a UV light for:

the quarantine of new fish
to stop an outbreak of Fish TB (which my article describes)
to eradicate green water algae
UV light bulbs are expensive and don't last that long. 

The extra sand layer probably would decrease the infusoria (protozoa that feed on substrate bacteria).


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## florida phish fan (Dec 3, 2020)

Thank you much, good to know. 

Brain cells aren't what they used to be - I swear I read somewhere that you felt running a UV light was a good "insurance policy" esp for those who may not have room for a quarantine tank or are... ummm... lazy? Not advocating laziness, just saying. 

I wonder if using pea gravel (like Caribe sea river rock - the one that's the size of pea gravel) might be a better option as it wouldn't smother everything in the soil? (infusoria/bacteria) 

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## sbalabani84 (Oct 28, 2018)

Hi, having a dirted tank planted mainly with Crypts I find this post very intriguing. My tank has been running for three years now. I have used small diameter gravel for the substrate and I also have a lot of stones so there is a lot of detritus trapped under the gravel.

This has caused some algae and a surface film lately. 

I too have noticed better results on my other smaller tank were I used sand as a cap.

I might have to try it!


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## johnwesley0 (Feb 23, 2021)

I'm wondering if one possible hack would be to start out with STS as a cap, enough that after a year it mightt break down a bit, if not completely into sand, enough to gradually work its way into the soil?


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## dwalstad (Apr 14, 2006)

STS is pure baked clay, it will gradually break down into smaller particles and work its way into soil.
There is no sand in STS.


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