# Thick substrate beds and Anaerobic Bacteria/Hydrogen Sulfide



## sarazorz (Mar 7, 2013)

Hello there, I had initially posted on another forum looking for answers to my questions - 3 hours later here I am trying again!

Today I started dirting my new 29g, and by dirt I mean Miracle Grow Organic. So I was dirting away, building terraces as planned, and I thought maybe I should check to see if too much dirt would be a problem. Sure enough, after some searching I found a few articles about thick layers of substrate and how they can be susceptible to Anaerobic Bacteria, which results in Hydrogen Sulfide gas pockets - which will crash a tank.

Then I also found a bunch of people who say this theory about the gas bubbles is "excessive", then I read about people who say "i have 8 inches of dirt in the back of my tank and it's fine", and other stuff that contradicts the dangerous thick substrate theory. Also mentionable that I watch Amano build tanks all the time (on YouTube) with super thick layers of substrate, which appears to be at least 6 inches and above, sometimes up to a foot of the stuff!

Here is a pic of what I was trying to accomplish (I have since removed the excess dirt and I'm back down to about an inch)










You can see that I'm trying to build terraces using a wall of rocks, filling in behind the rocks with dirt. Since I'm now terrified of thick layers of substrate, this is an idea I had as a solution:










However, I'm not sure if the same problem would occur with a thick layer of regular old gravel.

Basically I need to know how to proceed. Replies appreciated.

Thanks!


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## Michael (Jul 20, 2010)

Welcome to APC! 

This is a repeat of the private message I sent you, with some additional information. This is a good question that will interest many people. 

I think deep soil layers (more than 1.5") do cause problems, especially if you are using a rich, 100% organic material soil like MGOC. Deep gravel layers are not as bad, but can cause some problems as the small soil particles work down into the gravel. This eventually causes the same situation of organic material decomposing in an oxygen-poor environment.

The type of soil you use really does make a difference. See the sticky, "Suitable soils for the Walstad method" in the El Natural forum. MGOC soil has high nutrient levels, and is composed of all organic material that is not fully decomposed. This can create rapid anaerobic decomposition which produces hydrogen sulfide. A soil with less organic matter, or one that has been mineralized (see the threads in the Library), is less likely to do this.

Differences in soil account for some of the different experiences other people have had with deep soil layers. There are other factors, such as the type of plants in the tank.

To do terraces as in your design, I like to use ceramic tile, slate, or flagstone as the bottom layer. This gives you depth and topographic change for the design, with nothing deep in the substrate that will decompose. Well, almost nothing--a little soil will still work down into the cracks. Just put as many layers of the tile or whatever necessary to give the level change, then put the soil layer and cap on top of that.

Depending on the amount of level change you want, you can use big pieces of stone or solid brick to build up the terrace. None of this will be visible because it will be covered by soil and cap, or your rock wall.

To summarize, deep layers of soil are definitely not necessary, and can cause problems. Why not just avoid them to begin with?


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## Yo-han (Oct 15, 2010)

Excellent answer by michael. Only thing I could add is that Amano does use it but kostly short term. And if he uses it long term it is a more loose and less organic substrate than a dirt tank. Als with very few fish, excrements won't become a problem as fast as with most tanks. It is not as easy as comparing your tank with one of Amano or anyone else unless you use the exact same method and bioload and everything. So this is also why some people do thick substrates with no problems, others kill all their fish.


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