hair algae

[tomini]

hi everyone i recently got hit by a major hair algae problem
my parameters seem fine, i do a 5% w/c everyweekend on my 75 gal with r/o from safeway
and i have my pc's on for 12 hours a day
everything used to be fine for a year or so and now i cant seem to stop the growth ive even tried taking the rock out and scrubbing
i only have 2 clowns a mandarin, and a goby in there with some various inverts
what can the problem be???
any help you guys can give will be much appreciated