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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.