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Re: [APD] Re:Barr Method Question

The intuition that some folks have is that you keeping
adding but removing only some of the water so the buildup
must keep occurring.

As Paul points out, as the concentration goes up, the
amount removed with each water change goes up. I think
technically, if you measured everything exactly, the level
would rise infinitely but the increments get so small after
a relatively few water changes, that they are insignificant
-- especially when you consider that water changes are
rarely exact.

All of this assumes you aren't adding significant amounts
of nutrients from fish food, which msut be treated, for
these purposes, as a higher dosing level of some nutrients
(espeically NH3).

Scott H.
--- Paul Krombholz <krombhol at teclink_net> wrote:
>    Dale wrote:
> >.....Even with 50 % weekly water changes and assuming no
> plant 
> >up-take (bad assumption I know), the nutrient levels
> would continue 
> >to rise in the tank.........
> The nutrient level does not build up indefinitely. 
> Assuming you add 
> nitrate to initially give a value of 10 ppm, do a 50%
> water change, 
> then add the same amount of nitrate,  and that the plants
> don't 
> remove any, the level in the tank will  level off at 20
> ppm.  If you 
> do as above, but with 75% water changes, the content will
> level off 
> at 13.333 ppm.  With 25% water changes you level off at
> 40 ppm.  The 
> general formula appears to be that you level off at the
> initial 
> concentration times 1/(% water change)
> -- 
> Paul Krombholz in rainy central Mississippi---lots of
> rain!

S. Hieber

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