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Re: anaerobic substrates

Who said anaerobic substrates are a bad thing? There are several GOOD 
THINGS that happen when the substrate is anaerobic;

1. Ferric iron and manganese are reduced to ferrous and manganous forms. 
Both are more soluble than the oxidixed species.
2. As an added bonus, when iron is reduced, phosphates are liberated from 
the ferric oxyhydroxide colloids that are formed under aerobic conditions.
3. It is true that denitrification occurs but under anaerobic conditions 
nitrifying bacteria can quickly fix N2 into organic compounds. The result 
is an increase in ammonia. This is beneficial since studies have clearly 
and consistently shown that aquatic plants prefer ammonia over nitrate.
4. Aquatic plants in a natural setting ALWAYS have their roots growing in 
anaerobic substrates. They have adapted to these conditions and indeed 
some species can not produce root hairs UNLESS the substrate is anaerobic.
Additionally, repeated studies with a wide variety of aquatic plants have 
shown that plants grown on fertile substrates ALWAYS grow significantly 
better than those grown on sand ...even when a full complement of mineral 
nutrients is supplied in the water column. Its amusing to me when I see 
all this time spent on CO2 injection (especially by beginners) in an 
attempt to optimize growth when the fundamentals such as light and substrate
have not been addressed properly.

BAD THINGS that can happen;

Gases such as sulfide, methane, nitrogen or combinations of these can be 
formed. The solution is to take the soil you want to use, put it in a 
large pail or tub, and submerge it for several weeks. Observe carefully 
and if you smell sulfur compounds then try another substrate. Eventually, 
like Paul Krombholz, you will find a process that works for you (even 
with the unlikeliest of substrate materials :-).

A large nutrient release can occur as the substrate becomes anaerobic. 
This may cause algal blooms. Again, to deal with this problem, submerge 
your substrate in a large pail and let it sit for some time. Another 
solution, of course, is to place 1" to 1 1/2" of coarse sand on top of 
the fertile substrate to act as a seal.