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Discussion Starter · #1 ·
Hey all!

This is my second run at a planted tank, so was a little bit more analytical with my approach, and I think it turned out great!

I posted the pics on another forum, and a user commented on how much substrate was in the tank. I did 3.5-4" depth throughout the whole tank since I planned to have a few rooters like swords in the back and crypts up front. Then plant mid with a bunch of stems.

I was under the impression for good sized rooters, a depth of 3"+ was good, but cautioned not to go too deep. Now I'm reading most people slope and all that, so they don't have a true 3.5" or 4" substrate depth. The reason why I didn't slope is most of the foreground is all crypts and dwarf sag, so I didn't want to root bound them.

Is 3.5" excessive or any cause for concern? Or just an esthetics preference not to do it this way?

Thanks!
 

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It depends on what substrate you're using. If it's large enough granules that it won't compact, you'll be fine. If it's super fine, like play sand, you may have some issues in places that don't have plants.

The concern is always anaerobic bacteria. When anaerobic bacteria break down Nitrates, the byproduct is Hydrogen Sulfide (this is the rotten egg smell you get in swamps), and it's poisonous to your fish. The reason this isn't a concern where you have plants, is because your plants will produce oxygen from their roots. This will prevent anaerobic bacteria from growing.

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The short answer is you are fine and not to worry about it.

The longer answer is that the internet has been going on about gas buildup murdering fish for a long time (I used to believe it as well). But the reality is that this is pretty much nonsense. I've personally run tanks 8" of sand without any issue. There are folks running tanks deeper as well with no issue. There are professionals commonly building out large tanks with 12" or more of substrate be it sand or aquasoil or a combination of both and there are no issues and doing it on youtube.

There are people purposely cultivating anaerobic bacteria in filters to convert nitrogen into a gas and those people have no issues.

For that matter I've seen shallow ponds (1 or 2 feet deep) with lots of fish in them and of course the 'substrate' is just straight dirt since you know.. its a pond and still all the fish are alive.

Deep substrate creating fish murdering gas is the internet aquarium boogeyman. The biggest reason to my thinking for not going too deep on a substrate slope is the stuff doesn't stay put and wants to level out over time. So long as your slope is shallow enough, or better yet, you use some rocks to create a barrier, you can go as deep as you want.
 

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Discussion Starter · #5 ·
It depends on what substrate you're using. If it's large enough granules that it won't compact, you'll be fine. If it's super fine, like play sand, you may have some issues in places that don't have plants.

The concern is always anaerobic bacteria. When anaerobic bacteria break down Nitrates, the byproduct is Hydrogen Sulfide (this is the rotten egg smell you get in swamps), and it's poisonous to your fish. The reason this isn't a concern where you have plants, is because your plants will produce oxygen from their roots. This will prevent anaerobic bacteria from growing.

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Good to know! The tank I would say is pretty heavily planted (I like the overgrown look). This is a relief. I use a medium grade black diamond blasting sand, so it shouldn't compact at all.

Would the swamps having a much larger amount of decomposing material prompt more anaerobic bacteria forming? And because we do water changes to pull nitrates and basic maintenance to remove most solids that it just doesn't become an issue? Or am I over thinking it?

Bump:
The short answer is you are fine and not to worry about it.

The longer answer is that the internet has been going on about gas buildup murdering fish for a long time (I used to believe it as well). But the reality is that this is pretty much nonsense. I've personally run tanks 8" of sand without any issue. There are folks running tanks deeper as well with no issue. There are professionals commonly building out large tanks with 12" or more of substrate be it sand or aquasoil or a combination of both and there are no issues and doing it on youtube.

There are people purposely cultivating anaerobic bacteria in filters to convert nitrogen into a gas and those people have no issues.

For that matter I've seen shallow ponds (1 or 2 feet deep) with lots of fish in them and of course the 'substrate' is just straight dirt since you know.. its a pond and still all the fish are alive.

Deep substrate creating fish murdering gas is the internet aquarium boogeyman. The biggest reason to my thinking for not going too deep on a substrate slope is the stuff doesn't stay put and wants to level out over time. So long as your slope is shallow enough, or better yet, you use some rocks to create a barrier, you can go as deep as you want.
I guess applying logic to real world applications sensibly debunks this internet fallacy a bit too. Why wouldn't it be a common problem in a real world application? (minus rare situations I'm sure) I'm sure there's far more decomposing matter in a pond and far deeper substrate, and some super compacted.

While not as aesthetically pleasing as a sloped substrate, I decided to keep mine level at 3.5" across the whole bottom since I tend to plant so many root feeders. The rocks are actually a great idea... I don't know why I never thought of that to create a retaining wall of sorts... I might have to go back and replant the back. Great suggestion! Thank you!
 

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There is also the use of malaysian trumpet snails as an option to prevent buildup of anaerobic gasses, though there are drawbacks to that (namely that you will never be rid of the snails, and they can multiply quickly if not kept in check by some kind of predator like assassin snails).

I have MTS in all my tanks, and they do keep the substrate cycled, but keeping the shells of the ones eaten by my loaches and assassin snails cleaned up is a little tiresome sometimes.
 
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