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Re: Rock PO4

Ken, then Tom Barr wrote>

>> I have significant amounts of phosphate in my tap water (> 1 ppm I have not
>> tested it on the high range of my test kit.).  When I do a partial water
>> change it is gone within a few hours.
>So where does all the PO4 go day after day? How much can the gravel possibly
>hold? Must all go to the plant at some point.

Not necessarily....
If the gravel has laterite (or lateritic soils), it can hold alot. In the
aerobic portions of acidic iron bearing substrates,  ferric ion will react
with inorganic phosphate. The resulting phosphate compounds are highly
insoluble and tend to stay in the aquarium bottom.  When the substrate is
disturbed, the small particles can become suspended in the water column.
These suspended iron particles will also react with phosphate. The
insoluble iron phosphate compound can then accumulate in the substrate.
This interaction between iron and phosphates is used as a basis for
advanced waste treatment methods for phosphate removal from domestic

Boyd has studied pond water using an experimental pond (over 20 years old
without renovation at Auburn University in Alabama) and reported water
phosphorus concentrations of 0.04 ppm with a soil bound phosphorus of 1000
ppm!! He found the concentration was greatest at a depth of 1-2 inches.
This was an experimental pond  in Alabama.  Just below the surface, the
phosphorus concentration in the water surrounding the sediment particles
was one ppm while the adjacent surface water was one tenth that value. 

This is described in more detail in my PAM article.