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Re: [APD] Re: Nutrients, Water Changes, Etc.

On Tue, 4 Jan 2005 10:19:22 -0800 (PST), S. Hieber <shieber at yahoo_com> wrote:

--- "William M. Cwirla" <wcwirla at verizon_net> wrote:

. . .

2.  I'm wondering about long-term build up of residual
salts due to
regular dosing of fertilizers.  Most of the nutrients we
add are
chloride or sulfate salts.  While the potassium,
magnesium,  etc. are
utilized by the plants, the counter ions are not (except
in the case of
KNO3 or KHCO3).  Presumably, there will be a long term
build up of
sulfate and chloride salts in the water column.  A 50%
water change
will not offset the additions.

Actually, they pretty much will. You end up taking an awful
lot out with the changes and the build up levels off toward
infinity. Larger changes would cause things to level off
sooner but 50% is probably the most that anyone needs.

Scott H.

Provided you have a fairly constant rate of fertilisation, and are doing some waterchanges (any amount, in fact), then the level of the nutrient will always tend towards a FINITE value, not an infinite value... even if you are only changing a tiny fraction (ignoring evaporation). Of course, the more you change, the lower this value will be. This is also assuming that the nutrient is not being produced or used; obviously if it is being used then it is even less of a problem. If it is being produced, I can't remember if it tends to a finite value or not. Also I think chloride and sulphates are nutrients; certainly the sulphate is. As are phosphates etc.

Andrew McLeod
thefish at theabyssalplain_freeserve.co.uk

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