# Substrate Depth - How deep is too deep?



## Manwithnofish (Mar 12, 2008)

I have a 70 gallon fw planted tank which I started 4 weeks ago. It measures 36"l x 18"w x 25" h. I decided on a mixture of Eco-Complete and Flourite (lfs had a beautiful show tank and that's what they used and recommended). I googled "substrate depth in aquariums" and the first three hits talked about depths 3",4",...6" or more. So I found an online substrate calculator and decided to use 40lbs (2 bags) of Eco on the bottom, then 3 bags of Flourite (45lbs) then I mix one bag of each for the top. I mixed it for asthetic appeal (I liked the mixed colors). So all together, I have about 120 lbs of substrate. It amounts to about 4" deep and looks good in the (tall) tank. I have received the full spectrum of feedback on this question on other forums. Some exclaimed that my tank would explode while others proclaim that substrate can be over a foot deep (as long as it isn't sand or something, i.e. particle size matters). The debate centers around the issue of methane and hydrogen sulfide gas generation. 

According to what I have read from Diana Walstad's book (text summarized from book): 
(1) H2S (Hydrogen Sulfide), a resulting byproduct of anaerobic decomposition of organic matter (in the substrate) can be extremely toxic to plants, but not fish because it is oxidized immediately in the presents of oxygen in the water. H2S is oxidized aerobically by chemoautotrophic bacteria. So my take on this is that there's probably no need to worry about the H2S unless I see all my plants die from black tipped roots.

(2)Methanogenisis is the process where Methane is produced by anerobic bacteria in the breakdown of organic matter during the fermentation process and is released from the substrate and enters the water. Methane-oxidizing bacteria are apparently plentiful in the tank (on the surface of the substrate ) and quickly breakdown the Methane. I think this takes care of the Methane being released by diffusion (slowly) into the water. Aquatic plants facilitate the breakdown of the Methane by increasing the amount of the oxidizing bacteria. So the danger appears to be in gas pockets or bubbles that might accumulate in the substrate and then for some reason result in a sudden and large release of Methane. If I want a deeper substrate, can I mediate the danger of this happening without taking an eggbeater to the substrate or adding a billion Malaysian Trumpet Snails? Is there a threshold depth where the probability of disaster doubles or triples?

I guess I am trying to get a handle on what is "too deep" and a threshold depth at which these problems become certain. I expect it's probably a linear relationship of increased risk with increased depth. At this point I'm exhausted from the technical debate and I'm just trying to determine if I have passed that threshold limit and need to remove some of the substrate.


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## cs_gardener (Apr 28, 2006)

I don't think you'll have problems with the 4" as long as you're planning on plants with good root systems. Crypts, swords, Nuphar japonica, lilies, etc. will help prevent the build-up of anything bad, and those roots go _everywhere_. Some of these plants really grow better when they have more room for their roots than they do in shallower substrates where they are more cramped.

I normally use soil under eco complete and the combination of them is up to 4" deep in a couple tanks. While I do have MTS, I think it's the root systems of my bigger plants that really help keep things healthy.


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## Manwithnofish (Mar 12, 2008)

Thank you for the reply.


> While I do have MTS


 I had a bid for 25 (free shipping) for $9.99 but I cancelled it because an advocate of the little critters said that they are wonderful BUT their population will get out of control quickly. This individual said that 90% of their substrate was MTS. That turned me off, so I cancelled my order. Don't want to change the thread, but I'd be interested in hearing your views on MTS. I'll open another thread later if I need to. Thanks.


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## cs_gardener (Apr 28, 2006)

My populations are a pretty good size, but by avoiding overfeeding I can prevent a population explosion from taking place. If it seems like I'm getting too many (hasn't happened in while), I bait them by putting blanched zucchini, an algae wafer, etc in a net or container on it's side on the bottom of the tank in the evening and pulling it out in the morning. 

In the areas where food regularly falls to the substrate I can see more of them than in less well-fed areas. So in the well-fed areas, the surface of the substrate may look like solid MTS with some plants sticking up, but not over a large area or in any depth. If I really didn't want to have them up front and center I could start feeding my fish from the back of my aquarium and have the MTS congregate back there instead.


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## dwalstad (Apr 14, 2006)

Manwithnofish said:


> I have a 70 gallon fw planted tank which I started 4 weeks ago. I decided on a mixture of Eco-Complete and Flourite. It amounts to about 4" deep.
> 
> 
> > Four inches of Eco-complete/Flourite shouldn't generate much H2S toxicity.
> ...


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## Manwithnofish (Mar 12, 2008)

> Whether the plants can grow with so little organic matter is another question.


So, just when you think you are beginning to understand something, about face 180 degree turn.

I thought my problem with the Eco-complete was too many nutrients, too much organic material for decomposition. People described it as a "rich" substrate. What is Eco-complete, gravel in "black water" (whatever that is)? I suppose I could try Flourish Excel maybe to supplement Carbon or is that even worth the effort?



> This is not a substrate I'd recommend for NPTs, but it could work.


Am I correct to assume NPT is Natural Planted Tanks?


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## Tex Gal (Nov 1, 2007)

NPT does stand for Natural Planted Tank. It presumes that you use dirt from which the plants will get their nutrients. The detritus from the plants continues to enrich the soil and you end up with a little bio-system. You can read this sticky http://www.aquaticplantcentral.com/forumapc/el-natural/26458-what-el-natural-step-step.html and others in the EL Natural section of this forum.


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