you might check for phosphates. are you using ro water or tap. you might want to test the source of the water. i had a big problem with hair algae. tried everything to get rid of it. lawnmower blenny, tangs, water changes, sea hares...... but this is what i figured out.
i used tap water for 1 week because my lfs ro unit broke. after that week started to use ro again then started to notice the hair algae. i assumed thta i got it from the tap water, figured it would go away by itself. it got worse and worse. come to find out the water i was getting from the lfs was high in phosphates. so was my tap. i quit buying water ffrom them and found another place to get my water. 1st i checked for phosphates. it was good. i did several water changes to get my phosphates back down to 0. in the mean time i bought a lawn mower blenny. he didnt even touch the algae.....made me so mad. well he ended up swimming up the power head.that wass ugly......when i started to notdice the algae wasnt getting worse and ym phosphates were at 0 i bought a sea hare.this thng is ugly but it ate all the hair algae. i do have to warn you tho. sea hares are posinous to the tank if they die in your tank. they will let off a dye and it will kill every thing. the best way to do it is to put him in for a week or so and monitor him very closely. when his job is almost done take him out and back to the lfs. they will only eat the hair algae and if you leave him in there after all the algae is gone he will starve. my lfs actually has a loan-a-hare. its preety cool! any ways i hope this helps and best of luck.