Zoas not opening and covered with algae

[ScubaSteve]

Check to see if anyone nearby is stinging them as that's kind of what it sounds like to me. Is the reddish-brown algae kinda gooey (like cyano)? Keep blasting the "algae" off with a turkey baster or a powerhead and try to remove any nearby stressors. If it persists I have found vitamin C to help recover from this but DO NOT use this until you really understand what you're doing.

PM ZoaElite and see what he has to say.