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?

[Aquattro]

I've always used Hanna, never not trusted what it told me. My reagent is the same batch yours was. If I read 0.1 and do a 50% water change, it says ~0.05.

[DSlater]

Yup. Would have said the exact same thing a month ago.

[rayjay]

Can't help with a recommended test kit as I've not tested for phosphates in about 20 yrs now. I tested when I first started the hobby but then realized that I was ALWAYS adding phosphates every time I feed the tank with anything so why bother.
I didn't have to test to know I had a problem as I could see the changes in the tanks.
If my husbandry protocol wasn't sufficient for the various maladies that could arise, I changed my protocol to what would be sufficient.