Tank Dying, Need Help ASAP

[ThatSharkJake]

So I left to go on vacation about two weeks ago and the tank was fine, but when we came back about a week ago the tank was looked like this. The corals are dying but the fish seem okay.
We’ve been doing water changes every couple of days and our ammonia, nitrite, and nitrate levels are fine. Could it be silicate or some form of bacteria/algae?

 

[death-by-reef]

need parameters
#reefsqaud

 

[death-by-reef]

also a pic under white lights

 

[V A R I A N T]

How did you account for evaporation while you were away? Did anyone care for the tank or was it left unmanaged? You asked a loaded question with little information, so be prepared for a lot of questions from those looking to help.