I might be a little late chiming in on this one but, I had been having the same problem recently. I finally decided to get some different lighting. I tried pure actinic because I had heard that plants and algae couldn't use that type of light. I got home and tried them but I did not like the color of them (too blue). I took them back and got some 50/50 "reef sun" bulbs. The colors from these bulbs are much better. I also cut back on my feeding a bit and increased my water changes. I can't actually check my nitrate levels at the moment because that particular solution bottle in my test kit broke open and spilled everywhere about two weeks ago. Anyway I did all these changes about a week ago and so far so good. I can not say for sure if any one thing was the one that did the trick. But with a lighting change, more frequent pwc's, and a cut down on feedings, my problems seem to be solved.