Toadstools not opening

[JBAqua]

I started my first reef tank (29 gal BioCube) last August and have progressed slowly with it. I have had the odd casualty (1 watchman goby and some peppermint shrimp) but otherwise everything has been doing well.

However last night my toadstools closed up and haven't re-opened today. I did a small (10%) water change to see if that would help but nothing.

All other corals are open and doing fine. Other corals are: Kenya Tree Coral, Brown Button Polyps, Gorgonain, Devil's Hand, and one small one which I can't recall the name of.

Any ideas as to what the issue might be?