I just feed mine Phyto and they are multiplying like crazy. I started of 3 months ago with 5 polyps and now I have around 80 polyps under Power Compacts. I am installing T5 lighting on my tank on Tuesday so they should start growing even faster.
i dont feed mine, once in awhile they grab a flake or two but thats about it
they are spreading and growing pretty fast. but the first few months you have them they wont grow, ya gotta give them time then they take off like weeds