I am using the Salifert PO4 testkit. I totally agree that the colour coded test kits suck. I think the colorimetric meters are too $$ and only test a few things (PO4 not being one of them). There is a MERC Phosphate Test Kit ($79.95 at J&L). With the kit you can measure phosphate levels within the range of 0.14 – 0.008 (P) which equates to 0.43 – 0.023 (PO4 ). My goal is to get the PO4 levels down so the tube is clear which should indicate a PO4<0.015. Time will tell.

p.s. I did see refills for the MERC kit advertised on a CDN LFS website (not J&L) but can't remember which one.