I'm new to saltwater, in fact just started about a week ago. I purchased some rock that had been dried out from a tank at a reputable local saltwater only store. After only a few days of it's new home in my tank it has developed this white cotton looking stuff growing on the underside of one of the rocks. My question is, what the heck is it? Should I take the rock back out? Any help would be much appreciated. Ammonia 0.25 Nitrite 0 Nitrate 0 PH 7.8 and tank is 75 gallons with 6 Damsels. I have a picture of it but for some reason not letting me upload it. If I figure it out I will post it.