Eesh... that's not good about your LFS. Maybe you should start working there?

I have never fed my mushrooms anything special at all, and they are spreading and growing like crazy in my 12g nano. After having the tank about a year and a half, I've had to frag them multiple times because they're taking over! (They squirt water at my fiancee though as if to protest, whenever he takes the rock out of the water... pretty funny).
They'll go through periods where they just look "blah" and sometimes might excrete white stringy material out into the water... from what I understand, that one "mouth" also serves as their "exit" so don't be alarmed. They just get moody.

Keep us updated, and good luck!