I battled hair algae in my 90g for longer than I care to mention...
.
I played with lighting, feeding, manual removal...it kept comin' back. With your tank still being young, algae will have cycles. My culprit ? Insufffient biological filtration. I replaced a canister filter that was long since removed as I wanted to slowly convert to a reef set-up. I had a lot of live rock and a lot of flow so I figured it was "good to go..." Ammonia and/or nitrates were never detected but they had to be the source of the problem ? The algae was gone in four weeks and the coraline once again flourished. I really missed the hairy look so I again removed the canister filter and I was glad to see the rapid return of my hair...
. The canister is again back on and I'm goona' settle with a fish only system.
Good luck and be patient...