This will do it. Actually, anything for phosphate readings over 0.06 can cause algae issues.
My Salifert test kit lists results as follows:
0.10 - critical
0.25 coral growth retarded.
I know that when we fought our cyano
battle back at the beginning of the year, we pretty much narrowed it down to *elevated* phosphates - which, at the time, were just shy of 0.10.
I'd try to increase water circulation/flow as much as possible (cyano
thrives in low flow areas), but I'd also look at (1) testing your makeup water for P04 -- if you're not using RO
, you could be introducing phos. with your water changes. (2) - Look at how much you are feeding, how often, and what you are feeding (including all additives).
If you're not adding P04 with your water changes, do a series of 20%, twice-weekly water changes, siphoning all visible cyano
(if any returns) from the tank when you do so. See if that brings your P04 level down.