Black brush algae..excess phosphates?

I have been battling BBA for a while now in my 55 gallon freshwater
tank. I know that excess phosphates are one contibuting factor.
Untill recently I was unable to find a test to tell me what my
phosphate levels were.

Well, I finally found a phosphate test and it says that the phosphate
levels in my tank are 2 ppm. I also tested my tap water and the levels
are the same (2 ppm).

My question is, what level of phosphate is considered "excessive" pr
high...does BBA need a certain level in order to thrive?

I have recently purchased some "phosban" and put some into my canister
filter. The next day my phosphate level was at 0.5 ppm.

Any information is greatly appreciated. Thanks.