I had brown algae then it turned to red slime algae or ciano bacteria for about 45 days, the day i decided to use chemclean it just vanished itselt in 2 days, so my experience says just wait and it will be fine, few tips u must consider, dont over feed, wash the food, light quality and duration, uv. Btw i dont do water change at all, i have tried water change for 2 years, and without water change for 3 years, and im more success with my live stock without water changes, i focus on water movement and i find it really good, yes tangs are very good cause they eat fish waste also gobbies and clams