Dry-Tab Phosphate tests

> I bought a Dry-Tab Phosphate test kit the other day, and have tested my
> aquarium water several times.  Each time the solution remained clear (as in
> zero phosphate), but there is a dark blue precipitate at the bottom of the
> tube?  Does anyone know if this is normal, and I indeed have very low
> phosphate, or something is wrong with the tests?

You have low phosphate. The precipitate at the bottom doesn't count
so don't shake the tube up, just let it settle and judge the color
of the water. When you have substantial phosphate, the water will
get a strong blue color however if your aquarium water had this
much phosphate and light, it would probably turn into green soup 
in 2 days. I'm not sure if these kits are accurate enough at the
low concentrations of phosphate we're interested in. Apparently
P doesn't stay in solution very long before it is grabbed up by
algae or plants.

Steve in Vancouver where it's raining (still)