Having a battle with green hair algae >:(

[mandyplo]

Battling an intense green hair algae problem... Each day is so much worse than the last.
It feels like this happened over night and got out of control. Not sure how it started, I am running RO/DI water and always have, I run dual canister carbon and GFO filtration, sump with protein skimmer and filter floss. 60+lbs live rock filtration (not base rock, live rock). Kessil A350W LEDs (2 of them). I do 25% water changes every 3 weeks and test regularly. Phosphates undetectable. 1.024 salinity.
Really don't know what to do! Some people have suggested acquiring a tang but that's not going to solve how the problem started in the first place...
I only have 3 fish and am not over feeding (pellets once sometimes twice a day).
I want to try putting some chaeto in the sump and seeing if it will out compete for nutrients... Any other suggestions I'm at a loss