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Re: bubbly substrate
> >> Or perhaps this is a good thing that will reduce the nitrates? <<
> This won't reduce nitrates. If the soil was fertile and contained
> organic materials, it may increase them. Since discus are normally fed
> well, you'll probably be getting plenty of nitrogen from the fish food
Well, there might be a nitrate reduction.
As the Eh of a soil drops there are three common anaerobic reduction
stages. After oxygen is entirely reduced, nitrate is reduced (mostly) to
nitrogen gas, then sulfate is reduced to sulfide and finally carbonates
are reduced to methane. All of these steps are performed by bacteria;
those that reduce nitrate are often facultative anaerobes and can live
with or without oxygen, but I think the sulfur reducing and carbon
reducing bacteria cannot survive in the presence of oxygen.
Most soils are heterogeneous, so it is possible for all of these processes
(and aerobic processes) to occur simultaneously in different but sometimes
barely separated areas of the same soil.
In order for sulfur reducing bacteria to live, the conditions for nitrate
reducing bacteria must already exist. So if you do get hydrogen sulfide
gas or methane from your substrate then its almost certain that there will
be some nitrate reduction as well. Just how significant that is depends
on how much circulation there is in the substrate. But I really wouldn't
expect that a substrate capable of reducing sulfate or carbonate would
also be a source of nitrate.
If a substrate starts bubbling and the bubbles _don't_ stink I would tend
to suspect nitrogen gas rather than methane. Water in contact with the
atmosphere is already at about 80% saturation with N2, so it isn't
necessary for the bacteria to produce a lot of nitrogen before the water
becomes saturated and bubbles form. Also, the conditions necessary to
produce nitrogen are much less extreme than those needed to produce