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[APD] RE: [AGA Member] old soil substrate from a planted tank

Richard Schiek asks
> The old substrate had a rotting smell
>   I assume that this is bad

No its ok, the smell is quite normal for any substrate, particularly a
soil substrate. The tank stopped being productive because you probably
ran out of nutrients that had initially made it grow well. A soil
substrate can supply a lot of nitrogen for several months and this helps
to support rapid growth. Unfortunately, the nitrogen often appears as
ammonia, which can sometimes create a green water bloom. Nitrates are
not as easily assimilated by unicellular algae but are readily used by
aquatic plants. Often all you need to do is begin dosing nitrates and
growth will begin anew. The soil provides abundant phosphates, iron &
trace minerals for years but is not a good long term source of nitrogen.
As Thomas Barr has pointed out, dosing nitrates regularly & keeping CO2
levels high is an excellent way to have a highly productive tank. Soil
also supplies CO2 for several months as the organic matter decays but
this CO2 production declines over several months too so CO2
fertilization becomes more important, especially in "high" light tanks.
You can consider anything over 1.5 watts/gal to be in the high light
category IMHO. Others may disagree on that last point. :-)

I continue to use soil+peat+micronized iron substrates even though they
tend to be quite messy, and somewhat prone to algae problems. But they
usually produce excellent results especially with Crypts. Peat seems to
counteract some algae problems, possibly by releasing humic acids into
the water. My theory on the micronized iron is that the reduced soluble
iron in the substrate reacts with reduced phosphates to precipitate
them, thereby keeping the P available only in the anaerobic reducing
areas of the substrate where they are preferentially available to rooted

I also like to feed the roots with Osmocote (ammonium-nitrate) inside
clay balls for those plants that I want bigger such as a Black Sword,
Lace plant or other Aponogeton. Feeding N at the roots can reduce the
amount of extra trimming you have to do on stem plants, which can grow
like weeds if you are feeding N in the water heavily. What I mean is you
can slack off the hydroponic N dosing and still keep that favourite
centre-piece plant flourishing.

Is heavy growth a problem with most folks? Or am I just
complaining/bragging? :-P

Steve P

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