I would be happy if I had that level of phosphate in my tank. It's at 0.1 and has been for a long time.

Do you run GFO?

I can pretty tell how much P04 I have by how fast the algae grows on my glass. When it gets up to .1, I change my GFO, and then it is again down to between 0 and .04. It slowly creeps up over about 2 months, and then I change it.

I only use about 200 ml of HC GFO in my reactor. I also give my reactors (carbon and GFO) an air bubble flush when I clean the 1st canister, which then stirs up the GFO, and the levels drop down again. But when the P04 stays up, then I know it is time to change it.

I also run a bio pellet reactor (N03 always zero now), so it may take out a bit of P04, too. Lately, though, I have really let my bio pellets run low in this reactor (only about 200 ml in it now), but will not add any until I start seeing some nitrates again.

And to think that 2 years ago, this same tank had over 50 ppm N03 (as high as 100 at one time), and P04 at 1.0.