I technically have an airstone powered protein skimmer in my tank, but its been kind of broken for a few months now (i've been too lazy to get a new airstone). So pretty much since about summer my tank has been skimmer less. Still pretty good growth on most of my corals, I've been having some minor issues with my monti that i'm hoping to figure out, but its gotten good growth still so i don't believe it has anything to do with the lack of a working skimmer. As far as my mushrooms are concerned, I noticed no difference with them without the skimmer. They were doing well before, and they are doing well now. Tank is 29 gallons, sumpless, I keep ricordeas, discomas, an acan, a favia, a monti (branching), and a cyphastrea.