I had a seahare a while back that did wonders, gave him to a friends cause im out of algae. and I always keep a very heavily stocked CUC. But last year had the same situation that you do, and I was close to breaking down the tank. But I read on here someone had luck with marine algae fix. I dont like to really dose anything but I really do believe it saved me in this hobby. I dosed for 2 weeks and have not touched it or had any issues since. Everyone survived the dosing cept for the algae You didnt mention what kinds of lights you have or age, and have you done a black out to try to kill it off? Not sure if i missed it are you doing Water changes? with RO/DI Im surprised the tangs arent eating it... Mine Love it but last year it was at a point that no one could make a dent in it, Im assuming like you are now.