Eh my shroom does that a lot--one day he's nice and HUGE, another he's barely enlarged...others, he's folded up. Shrooms are the hardiest of all corals so if your other corals are doing fine I wouldn't worry about it. If a tank ever crashed, shrooms would probably outlast all the other corals =P...it's probably just going through a phase...corals have moods too! lol...