Substrate Gas Pockets

[backtotropical]

This came up in another thread so i thought i'd post it here to get a definitive answer.

Almost every fishkeeper has heard of the poisonous gases which can accumulate in the substrate if it's not raked through every now and again, right?

I personally have never heard of it happening to anyone, and wonder if it's a myth?

If it's true, how deadly is this gas to the fish (and humans for that matter), and why do you never see a post on here titled "Help, deadly substrate gases killing my fish". Can you see it bubbling through the substrate? I just don't know.

Can anyone shed any light on this?

 

[Bignose]

I've posted this a few times over the years, so here it is again:

The main concern people have about sand would be anaerobic bacteria build-up. Anaerobic meaning without air, though more accurately, without oxygen. If you didn't know, the ammonia and nitrite reducing bacteria require oxygen to work (to convert ammonia to nitrite and to convert nitrite to nitrate).

Anywho, under anaerobic conditions, bacteria start to get their energy from other sources, like reducing sulfur instead of oxygen. And a by-product of that is hydrogen sulfide, yes, one of the deadliest compounds in nature.

But, there is relief. In water, as soon as hydrogen sulfide comes into contact with any oxygen, it will become harmless. So, even if there is a pocket, and even if you accidentally stir it up, it will become harmless as soon as it hits your well-oxygenated water. And you know your water is well-oxygenated since your fish are living in it, and they need oxygen. This is the stinky smell you got, sulfurs, but you most likely smelled sulfur oxides, not hydrogen sulfide. Like I said, hydrogen sulfide decomposes very quickly in the presence of oxygen while in aqueous solution.

So, there really isn't anything down there to worry about, so my recommendation is to not stir it at all. Just vacuum the top of the sand to get the uneaten food off the top. If uneaten food on the top is a constant problem, you probably should be feeding less, maybe a lot less. If it really bothers you, maybe decrease the thickness of your sand layer.

p.s. Another source of energy anaerobic bacteria may use is actually to convert nitrates to nitrogen gas. This is what living rock and living sand does for some marine tank setups.


Here is another quote from another post of mine:

Diana Walstad in her book Ecology of the Planted Aquarium actually talks about the beneficial aspects of having anaerobic conditions under the substrate near the plant roots. She has around several inches of soil as the substrates in her tanks. The anaerobic bacteria will use most anything for an energy source, reducing nitrates is just one of them. The bacteria can also reduce iron, sulfur, manganese, and so on. The great thing for plants is that these reduced forms are much more easily taken up, so anaerobic conditions help the plants get their micronutrients.

 

[Waterloo Kid]

I recently decommissioned my garden pond. My filter pump was placed on top of 2 bricks, the type witht he recessed face (or frog in correct terms). AFter removing the pump I picked the bricks up. Immediately a large bubble rose to the surface. I very nearly dropped the brick and gagged on the horrible sulphurous smell.

Believe me, sulphurous gas build up can happen. I just doubt there's a large enough area within a typical aquarium for it to be a problem. Add onto that the apparent rapid oxidisation of HS and you can see, there's not too much to worry about. It just stinks!

WK

 

[kribensis12]

I think thats what killed my baby fish. I had a ten gallon with around 30 baby platy's. The were fine, and after a while i noticied this 4 inch tall bubble, and around 4 inches wide in the sand. After a while i got annoyed, and poked the bubble, and it exploded, the next day i only had 5 platys left, then they got sick and died..

 

[Rhykiru]

hm, i was just wondering about this question the other day too.

my tank has play sand in it and when i mixed it up, small bubbles came up...

 

[n3ont3tra]

Same, nothing bad has ever happened because of it, though.

 

[Rhykiru]

hm, i was wondering, the gas pockets break down ammonia and nitrite right?

Do you think this might be the reason for my problem? Like the gas breaks it all down so that my bb is not getting anything and when i mix up the sand, it goes away so then the tank doesnt seem to cycle until the gas pockets form again and it happens again and again.

Anyone understand me?

 

[Bignose]

hm, i was wondering, the gas pockets break down ammonia and nitrite right?

No. The aerobic bacteria do this. Anaerobic bacteria are present when oxygen is deficient, and in fact, anaerobic bacteria can break down nitrate into nitrite and ammonia and all the way to nitrogen gas for energy. But, they can also use sulfur, and the by product of that is H2S. But, like I said in my above post, in the presence of oxygenated water -- like if you stir up the sand -- H2S is neutralized very quickly.

 

[jourdy288]

I recently vacuumed the bottom of my aquarium, as I hadn't in a while, and boy did that smell! Rotten eggs. You guessed it.

 

[yorkcoparamedic]

Hello everyone! This is a very interesting post as it brings up the anaerobic bacteria found in DSB's. I have just set up a new 30g saltwater tank and used approximately 70lbs of LS to create a 3" DSB. I have been getting different opinions from people and most seem to think it was not such a great idea, but provided no reason for their concern. Any input would be really helpful.

Take a look at my post for details on my set up Set up post

Chuck S.