So i have some star polyps that have been doing great so far. They are about the only thing in my tank that have been thriving and as of 2 days ago they have completly recessed inside and all i have is the purple covering. Is this normal for them to do once and awhile or is something going on that I may not know about. I have another colony of stars that are out and doing well but i don't know what is going on with these in particular. Any suggestoins would help.