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Re: [APD] soil substrate.

Josh Bjork writes:
>> I try to feed the fish plenty.  From what I understand it wouldn't take
that many to supply adequate N and P.  As long as there's adequate K so
it's not the limiting factor.  I realize N can be limiting too but i'm
ignoring this at the moment.<<

I would urge you not to ignore the possibility of N limitation. I thought
the same thing: there's so much N and P in food that all I would need to
supplement would be K. I was totally wrong.

I feed my fish well. If I don't fertilize as well, my NO3 levels tend to
stabilize at 0.2 ppm, far below where they should be. (For comparison,
Diana Walstad recommends a NO3 level of at least 3 ppm, Tom Barr has
mentioned 10 ppm.) When NO3 levels are this low, my plants grow very

I know I have denitrification occurring. I can tell because when I cranked
my NO3 levels up to 20 ppm, I started getting detectable levels of NO2 from
incomplete nitrification. (This went away soon as my NO2-consuming bacteria
grew.) But I suspect that large amounts of the N from my fish food winds up
turning into N2 gas and going away.

If you don't want to invest in a test kit, many fish stores will do a NO3
test for free or a nominal charge. It's worth checking out.

- Jim

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