Sand is Turning purple

In my tank everything died because my light fell in, and now it has been sitting with about 3" of water in it. I have not had time to start it back up, and the sand is turning purple, where the sand is against the glass. I just want to know what it is and is it a bad thing.

Thank you
Algae probably. If you're not filling it back up or topping off, that salinity is sky high. Any reason why you're not either draining it or filling it back up? It's gotta start stinking by now!