I feel your pain, mine broke out in hair algae and I mean badddd. I have neglected my 75gallon ever since I started building the 180gallon upgrade but also paid the price. Lost a few acros, a lot of my lps has died back, and one of my anthias was infected with popeye. I felt bad about it for some time and have procrastinated fixing it due to work. I had 2 days off in a row and decided enough was enough, made some saltwater yesterday and did a 32 gallon water change (size of the brute container it was in). I also removed all of the rock and scrubbed the algae off with a cheap wire brush. Reassembled the rock in the tank and cleaned the power heads as well. Hopefully I nipped mine in the butt before the tank crashed. Check your nitrates; that was the culprit in mine due to lack of water changes they climbed up to a staggering 180ppm which snowballed from my skimmer cup overflowing a good 5 times since the last water change :(
Best of luck to you necat, try removing the rock and giving it all a good scrubbin. Hope that helps.