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Re: aquatic composts
>> Adding large concentration of soluble phosphorus will be worse than adding
>> N and probably result in an immediate algae bloom.
>Cetainly this could be true for some tanks. In my tanks I doubt that
>phosphorus is a limiting nutrient, so additions of phosphorus aren't
>necessarily a problem. Also, the N:P ratio in plants is higher than in
>most fish foods (I think I can attribute this bit to Diana Walstad), and
>high N:P ratios mean that phosphorus should be limiting. So if you
>are keeping fish and you aren't adding nitrogen fertilizer (forcing N:P
>high) then the tank probably now has a comparatively low N:P ratio.
I probably should have said "MAY be worse" :-)
So, I assume that you are not using much fish food and/or you are adding N.
As you say, this will help keep the N:P ratio high relative to amounts
provided by fish foods. Otherwise, I believe that the plants can modify
their ratios to match the environment. This can be verified by a analysis
of the plant's content. Nevertheless, I still think the placement of the
recyled phosphates in the tank is very important. If it goes back into the
water column, then watch out! Even small amounts of excess water soluble
phosphates in the water column (<<1ppm) can trigger an outbreak of green
water or other algae. You can test this by adding small amounts and
observing the result. This is because typical plants have a relatively high
N:P ratio. On the other hand, your vascular plants might become phosphate
sponges if their N:P ratio is extra high (due to luxury consumption) and
they are poised for rapid photosynthesis. Then the tank may really be P
limited as you suggest.