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Re: "Hot mulch" and ammonia

Edziu Iskra <edziu at cybernex_net> wrote:
> A pile with ammonia or other nasty smells needs only to be turned (over) to 
> give it some air. Regardless, I wouldn't use it for anything but an outdoor 
> hot bed -- and certainly not in an aquarium -- until it had cooled down,
> and was allowed to sit for a while after another turning.  If it's hot, 
> there's a lot of decomposition going on, and that indicates there're a lot 
> of undigested organics which would pound the ammonia level and nitrate 
> levels through the roof in an aquarium.

You should always be very careful of the ammonia level when using a new 
organic substrate which contains anything like compost, potting soil, peat, 
or even manure.
> And, for what it's worth, manure doesn't smell of ammonia, either.  Urine 
> does.

Ammonia will be produced during the decomposition of _any_ organic material 
which contains nitrogen under anoxic or anaerobic conditions. That means 
manure (with or without urine) of all kinds when left in a pile or in a 
bag. The amount of ammonia produced is dependent upon how labile the 
material is. Well composted material like peat or humus should not produce 
sufficient ammonia to be a problem; remember the plants will be using this 
as their preferred source of nitrogen. Ammonia will grow plants _much_ 
faster than nitrate will and I believe that ammonia in the substrate is 
preferable. Urine contains plenty of ammonia or urea already but you can 
definitely get ammonia without urine as Edzui clarifies later. My point is 
that people need to be able to distinguish the differences in smells from 
their aquarium substrate when they dig it up. An ammonia smell is not 
serious. An H2S smell is.
> Note, though, very rich materials like manure will always smell if they're 
> decomposed anaerobicly, which happens whenever an outdoor pile is too wet 
> -- a soggy pile doesn't get good air circulation.  I imagine that if you 
> mix a lot of such a rich material into your substrate, it won't get nearly 
> enough oxygen there, either, and you will produce all sorts of nasty 
> gasses.  In short, I wouldn't try using any "fresh" organics in an 
> aquarium.

You should not use "fresh" organics (ie uncomposted manure) since it is too 
rich and will produce HUGE amounts of ammonia, phosphates and other 
nutrients which will be bad for your fish and encourage algae. On the other 
hand, a substrate may be considered rich when it contains _well_ composted 
material such as peat or humus-like compost and even this is going to 
produce substantial amounts of ammonia. It may or may not be enough to 
create a hazard to fish but it will grow most of your plants like crazy. A 
"rich" substrate will also produce gases but unless its so rich that H2S is 
formed, these gases are not harmful. They are almost entirely methane which 
is not toxic since it's solubility is so low. The other gases which are 
produced are N2, CO2, ethane, ethylene and minute amounts of other alkane 
gases. The really toxic stuff is H2S and it won't be a gas; it will be 

In my 50g aquarium I get plenty of gas bubbles whenever I disturb the 
substrate such as when removing a plant. In the first couple of months I had 
high levels of ammonia (handled by biological filtration without problem). 
This substrate is now about 5 months old and still produces methane gas. The 
gas has no noticeable smell so I conclude that there is no H2S and not much 
ammonia being produced. To put it in perspective, the middle 1" layer of 
this substrate is about 25% by volume earthworm castings mixed with 
vermiculite and gravel. The earthworm castings are about 25% organic so the 
total percentage by weight of organics is probably about 5% which is 
considered optimal. The tank is densely planted and has high lighting, CO2 
and nutrients. At present there are about 30 small fish in the tank with 
light feeding and no biological filtration.

From: mccarten at pa_mother.com (niall mccarten) 
> Unfortunately, having too much organic matter in the substrate 
> can lead to the problem that Karen Randall mentioned where potted 
> plants in one of her aquaria developed severe anaerobic conditions.
> The result of too much organic matter can lead to H2S (hydrogen sulfide) 
> production which is toxic to fish if the concentrations 
> get too high.  The H2S also binds to Iron (Fe+2) to form 
> insoluble FeS (Iron sulfide) which removes iron from the system.

I agree 100%
> The bottom line is not to have too much organic matter in the aquarium
> substrate.

Precisely. Also that organic material should not be fresh; it should be 
thoroughly decomposed. If you were using compost, it should have the appearance 
of peat or soil. I think the "magic" number is about 5% organic matter by 
weight. This should be mixed with a combination of sand and clay or perhaps 
vermiculite. Vermiculite works well since it has very high porosity but it's 
prime disadvantage is that the tiny flakes can float around and settle on the 
plant leaves. The substrate I'm building now will use sand instead of 


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