Help! My 75 gallon tank has some strange algae growing on one of my hard corals (It's a skeleton of an Acropora cerealis). The algae is black and looks like a cocoon or a web. My snails don't seem to be getting rid of it. I've been trying to find a picture on the internet so I can identify it, but I've had no luck. It doesn't seem to be growing on any other decorations or the live rock, just this one coral. I tried to vacuum it but it didn't come off. Then I tried to manually remove it, but it seems to have come back stronger. Does anyone know what this could be?
Thanks,
Tracy
