Total Noob Question: Phosphate

[Enigma]

Being that I know the API phosphate test is garbage, and I've got bacteria and algae issues, I decided to pick up the Hanna phosphate checker.

0.02 ppm

I understand that falls within the acceptable range (probably because all of the phosphate is being used up by the algae and bacteria), but that seems high. I was hoping to see lower.

I run a ROWAphos fluid reactor. Is the measurement I've gotten an indication that it is time to replace the ROWAphos? Is 0.02 ppm really okay, or is this something needs needs remedied?