I have those purple mushrooms too, and they have yet to cause problems. I have Red Mushrooms though that started with one small one I got from Eli some time ago. They seem to be the same type as the Mutant Ninja Purple 'shrooms from Tony. To make a long story short, I had no problem for a couple of years. Then suddenly I was overrun with them. Some were four inches across. I had to remove the rocks one by one and scrape them off. I put a couple in my 10 gallon nano, and they are spreading there like maniacs. The purple one in there is not growing much. So it might be best to watch what you do with Mushrooms.
