Purple Hard Lumps on Acans

[Rabidwolf]

Had a poorly Duncan that had spent alot of time upside down in the sand whilst I was ill.
Was trying to bring it back but looks like the heads started getting Brown Jelly Disease so not taking any chances and chucked it.

As I was sorting this out i noticed some purple lumps on an Acan, noticed a couple of days ago it wasn't inflating like my others or as colourful.
But now noticed lumps on the edges or centre. Used my scraper to waft over the top to see if they would dislodge but nothing.

Touched them and they are solid and don't move.

Any ideas?
Photos best I can get.

 

[SurfTrack]

Just looks like coralline algae to me

 

[Rabidwolf]

They came out from the Acan mouth, it retracted them not long after. But a few hours later they were all out again. He's puffed up a bit now.