hi, i'm sorry i do not believe that phosphate test result?? just my opinion,are you using rodi water,? run 2nd uv ,kill water borne algae,could be iron,feed once a day,let go from this,first take 2 buckets ,remove 5 gal tank water,split water between buckets,scrub off algae,in one,rinse swish in other,put rock back ,