I have gone through 2 bad cyano phases, the first one was within the first year of the tank getting set up. It took a week of chemiclean to get rid of it finally. Just recently it all came back, and my sand bed was completely brown. Chemiclean again, but this time it didn't work, and because of that I think it was diatoms. I was sick of the sand being dirty, so I bought a pair of diamondback gobies to keep it clean. They do a very good job, and the sand stays clean. My only complaint is that when they really go at it for more than a few hours the water gets kinda cloudy to prevent other algae from taking over, I have 2 long spine seaurchins and 3 tuxedo urchins. THis is all in my 180 gallon. I am very much the "oh theres a problem, I bet I can put something into the tank to take care of it" kind of guy lol. I find that most often there is a natural solution to problems related to reef tanks