boofer, Exactly. I test zero phosphates and nitrates, but still get the brown reddish cyano bloom. It had gone away, but a skimmer change and not replacing the Phosban has brought it back. I ahve also had a bubble algae spike as it was introduced on a frag, and a soft fuzzy green coating. since replacing the phosban, the coating has seriously changed and is receding. I wish I had gone ro/di years back...