Do I need to get rid of this starfish?

[Timfish]

Looks like you have a mushroom problem.

Yeah, but I like that shade of green.

 

[Softhammer]

I’ve had asterinas for 20 years and not once ever have I caught them eat absolutely anything other than coralline algae. They park on purple algae and it’s dead and neon red when they move on. This has been debated for eons but I’ve never witnessed anything bad from them. Now there is possibly different species of them but none I’ve ever encounter that eat coral. Test the theory, pick one up, drop it on a coral. I’ll put money on the fact that they roll out. Doesn’t hurt to kill them but doesn’t hurt to leave them either. If you have an over abundance id look to other causes such as an over abundance of detritus. Clean tanks very rarely have issues.