Hi, New to this, but here goes. I started my dream saltwater aquarium a couple of weeks ago. Water has been great, fish great, etc. Added a mushroom coral attached to a rock today. As soon as i plunked it down in the water, something slimy crawled out of a hole, looks like a snail, it's about 1/2" long, and is now sliming it's way along the front of the tank glass. Any opinions as to whether it's a good witch or a bad witch?