The coral looks like a plate coral. It is pretty unhappy, I won't disagree with that.
Lets start with the basics of things to get this on the right path. The current substrate is crushed coral, I would suggest replacing it with sand since crushed coral gets all kinds of gunk stuck in it and leads to nitrate issues.
is a flow and nutrient issue, like stated. Use a turkey baster or something similar to suck the stuff out of the tank. It looks like there aren't any powerheads in the tank, so you will definately need some. This isn't jus for the cyano
bacteria, but coral need proper flow so they can feed from the water column.
Cut back on feeding and use RO
water so you can get the nutrient issue under control will start to solve the cyano
and hopefully prevent an algae outbreak, as they feed off the same nutrients.