Duncan Coral Turning Brown

[Wasajacob]

Can anyone tell me what is happening with my Duncan Coral!?! He’s been thriving new heads like crazy but now this, tell me what to do!

 

[blaxsun]

BJD?

 

[Wasajacob]

BJD?

I am new to reefing I should mention. A mushroom on a shell got knocked into it and they were touching for a bit. Is this what it would look like if it had been stung?