Help with an Aussie Scolly

[slough shark]

Looking for a little help.
Bought an Aussie Scolly a few months back and have been having a few problems with him lately. In the beginning he was a nice bright red colour with a white centre, probably about 5' across. Now he's shrunken up for a good part of the day, hardens right up and has these thorn looking things on the outer edge. Not to mention he turning a bit purple in the centre. I've moved him off of the sand bed into the lower part of my rock work now. I really want to keep this thing and have a healthy specimen, but not sure where to go from here.
Water params are good.
If anybody has any experience or know of a good arcticle I should be reading it would be much appreciated.