I'd recommend calibrating your test kits to see how accurate they are. Here is a link that explains how to do so.
http://www.plantedtank.net/forums/wa...solutions.html
As for the phosphates, it doesn't really matter, as long as it doesn't become a limiting factor (ie. there is enough for the plants). Just shoot for anywhere in the 1-5ppm range, and you'll be OK. Don't fall for the myth that phosphates cause algae. An imbalance or limiting factor (often co2) is behind most cases of algae.