[Delphinus]

I gave up on the Hanna photometer altogether, found it a very cumbersome way to test.

Never could get the powder to dissolve. I both called and emailed Hanna Instruments about this, they didn't really have anything profound to say about it (they basically read the instructions to me). Although I did finally get someone who said that's why you have the 3 minute timed reading, to allow the undissolved powder to settle.

Thing that really drove me nuts is I couldn't get consistent readings from it. But then I was getting way lower numbers than what you got, I'm surprised, you definitely seem to have unbound PO4 in your water.

I think, FWIW, the tester is better for measuring trends in the 0.x range (not 0.0x range like some people on RC were claiming. "Oh I added Rowaphos and my PO4 went from 0.08 to 0.06!" ... IMO those people aren't using the tester correctly. With a potential error of plus/minus 0.04, the only real significant digit interpretation is going to be in the tenths not the hundredths. Again IMO.) I think trending is probably more useful than understanding whether it's P or PO4/3- or P or P205... I don't know, that whole phosphate stuff is getting kind of low level chemistry if you ask me, I didn't quite get that part either.

Good luck sorting it out.