[stephane]

For How long did you have this problem alan

+ how your tank habitant look did the coral look fine?

tell us more about the tank? for who long it run
what do you keep what do you add wich light and what age the bulb. Wath do you feed?

But IMO patience and maintenance will do it and there the only way to go. but unless you tell more about the tank any recomendation has no value there to mutch parameter to covert and to much interogation and as I tell you before you need to find the cause because you always gone have problem of any kind

If you try to much you will stess only more you system and he will not like it

About testing phosphate most of the time it will
showing a big zero since the algea suck it azap
the test only work before the algea bloom after you dont see notting but algea algea algea algea.....