# El natural substrate depth?



## JoanToBa (Aug 23, 2018)

Hello fellow humans, newbie here,
these past months I've been researching the Walstad method but I don't seem to find an answer to my question...

Is it possible to keep a really deep substrate in a Diana Walstad method tank?

The reason to this question is because a few days ago I stumbled myself on an aquarium coop video about a store that kept their fish in planted tanks, and not only that, some had more than 6 inches or something of sand. Their theory behind that is that the anaerobic bacteria would help removing nitrates from the tank.

Video link: 




PS: I would have MTS in the aquarium


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## Michael (Jul 20, 2010)

Welcome to APC!

Deep substrates are not recommended in Walstad tanks. The soil layer can become anaerobic and produce toxic substances, mainly hydrogen sulfide. I didn't have time to watch the whole video, and don't understand the rationale for anaerobic substrate. Of course all substrates have microenvironments that are anaerobic and that is beneficial, but when large areas are oxygen depleted it causes problems.

The usual recommendation is 1" of soil and 1" of cap, slightly less in very small tanks and slightly more in large tanks with strong rooted plants. If you want the look of a deep substrate for aesthetic reasons, you can build up a bottom layer of some inert material like stone or ceramic tile, then put the soil and cap over that.

That is a cool fish store, and I love to see lush planted tanks in a store. Plants do an excellent job of water purification.


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## mistergreen (Mar 3, 2007)

Plants do a way better job at removing nitrates. A little anaerobic is ok but a lot would turn your tank into a swamp. I guess you can get away with a lot of capping substrate where you have lots of plant roots.


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## zolteeC (Dec 26, 2017)

I guess the potential downside risk is a little bit higher if you add too deep substrate.

Weather it causes trouble or not, I don't know. I used to have a tank where I kept the dirt recommendation (~~1") but I put several large rocks on top of the gravel. Plants were growing good and essentially the tank worked fine. However, after quite some time, when I took the tank apart and removed the large rocks, beneath them I could smell H2S (probably). I guess the reason why this did not cause issue is because there was enough O2 in water and in the surrounding areas to neutralize H2S toxicity.

Anyways, I guess it is no accident that the typical recommendation is ~1" dirt and ~1" gravel (right size).


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## JoanToBa (Aug 23, 2018)

Thanks for the help everyone!


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## mysiak (Jan 17, 2018)

I'd say that you might get away with deep sand, as it's mostly inert and detritus doesn't go too deep. However anaerobic conditions with soil rich in organics can create problems as already described. Nitrate removal is much easier with densely planted tank and/or floating plants (and water changes). It's not really clear how much of nitrates can be removed by such anaerobic bacteria (at least I couldn't find any relevant information), so probably not worth the risk.


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## JoanToBa (Aug 23, 2018)

Hmm, I hadn't thought about that, thanks!


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