Hey, just wondering if anyone has ever had a problem with a grayish to brown fungus (?) or matter on the bottom of a tank? I work as an aquarist at an Estuarium and our 300 Gallon nursery tank developed this weird grey matter on the bottom. It doesn't seem to be effecting the fish, turtles or crabs, but its an eye sore. I have tried everything; water changes, new sand/rock/shells, and the salinity is good, pH normal. So I thought maybe it was over feeding (when I'm not working), but that doesn't seem to help or hurt it. I siphon it out and its back the next day. I have only worked with salt water tanks until three weeks ago, so any advice would be great. Thanks!