I have seen this stuff come and go with my 7g reef....never in my 36g...knock on wood....but anyway it always seems to happen when i do a big water change....like more than normal.....but i started using Red Slime remover and it went away...i use slightly less than the recommended doseage and it works great.....never came back at all...i have inverts, fish and corals in the tank and it didn't kill a thing or have a bad affect to my knowledge.....the corals or shrooms, xinea,green star polyps, none affected...keep and eye on the protien skimmer if you use it.....Red slime remover can casue it to go crazy.....