Mushroom removal??

[Aquattro]

If you can remove the rock from the tank, scrape what you can and buy some muriatic acid at teh hardware store. Couple of drops on the remaining tissue, no more mushrooms.
Muriatic is weak hydrochloric acid, so handle with care. But without taking teh rock out, best of luck! You know that little chunk of goo that came off when you were scraping?? It will become a few new mushrooms in no time, likely where you can't reach them!