I got a lot of live rock with my tank setup I purchased through Craig's List and the guy said that he hadn't been doing great maintenance. The rock seems to have this tan, fuzzy stuff growing on it. I have no idea if this is good fuzzy stuff or bad fuzzy stuff. It certainly doesn't LOOK nice! I saw something about cleaning your rock with a toothbrush while the rock is in freshwater. I know I have some things growing that I don't want to kill off. Help please!