Gtownfish,
Solving the Problem may be what you need to do, rather than put a bandaid on it.Somewhere excess nutrients (Nitrates, and phosphates) are lurking.Causes, I.E. Food, Lack of Water Changes, Underskimming, try Getting it off the rocks one more time, Do a couple of 20-30% water changes, Skim pretty Wet to remove more nutrients.Keep the Cheato, in the sump preferably, it will help knock out those nutrients.
Do you rinse your frozen food before feeding?Thats probably the most common way to Introduce excess Nutrients.