Whoa holy cloudy water batman

[Beverly]

Pics look bad, I'm afraid

Dying/bleaching corals are going to release ammonia, which might explain the fish gasping.

Did you remember to use dechlorinator with last water change? Also, a 50% water change is pretty drastic. Was there a reason you did one so large?

I wish there was something I could do to help figure out what happened to cause such a catastrophe