Trumpet coral

[sassycake097]

Not sure what's happening with my trumpet coral. Week ago it was happy. Water quality is good and all of my other corals are healthy. Too little or too much light and or flow?? Any help is appreciated!
Lights: ai prime
Size: 20 gal
Before

After

 

[Mr. Mojo Rising]

Seems to be a lot of algae in the tank, are you doing water changes? What are the parameters? What intensity is the light? Have you thought of a powerhead for the tank, it doesn't seem to be much flow and the surface is very flat, seeing the clowsn swim up near the surface makes me think of low oxygen.