More RODI Help

[DSlater]

Straight tap water - 0.16ppm
After filter and carbon filter - 0.19ppm
After RO membrane - 0.13ppm
After DI Resin - 0.13ppm
Rejected water from RO membrane - 0.25ppm

These results would be believable if filters were old and resin was spent but all are new.

Went to another reefers house today and did some testing. His Salifert PO4 test kit read 0.00ppm on his clean RODI water, my hanna tester read 0.16ppm.

OK, now that I don't trust my meter I came home, opened a new box of reagent and tested tap water for kicks... 0.00pm

What other test kits do people use(and recommend) for PO4?