Yes it is in sheets. I was putting a new soft coral can that have cause it
Then most likely it's cyano
. I highly doubt the coral caused it. How old are the lamps in your lighting system? Old lamps promote problematic algaes, etc. Also check your source water for phosphate, cut back on feedings- just put some nori in a clip for the tangs, and try a few water changes(assuming your source water checks out ok) to start w/. Try doing a search on this site, and I'm sure someone who can provide more advice will chime in.
PS-Posting your water parameters including Ca
may be be helpful.