What is this thing?

[michael.cilia]

And whats wrong with it?

 

[Dkuhlmann]

Looks like a devils hand leather or finger leather. It doesn't like where it is. Could be water parameters, lighting or flow.

 

[cloak]

It looks like a very grumpy Lobophytum. Assuming your parameters are within reason and the lighting is sufficient, increasing the amount of chaotic flow the coral is receiving would probably be your best bet IMO. If the coral has a secure base then it can withstand these stronger currents. This will also help with the shedding process and keep the coral free from detritus, algae etc. GL.