What water parameters are fine...post the results. Do you check for nitrates and phosphates...these will fuel hair algae growth.
Its not uncommon for newer tanks to go through algae bloom phases. Often, the algae will bloom, last for a week or two and die off when it uses up all the nutrients. Now, this assumes that the nutrients are not being replenished somewhere along the line. Some tips for controlling algae....
1. Use RO
water, it should contain no phosphates, nitrates or anything else that algae may feed off of.
2. Don't overfeed. Only feed as much as your tank will consume in a few minutes. Most fish foods will add nutrients to the water that fuel algae growth.
3. Keep a good, diverse cleanup crew...a varied selection of snails, hermits and if you're bold a "reef safe" crab will help eat up the unsightly algaes.
4. Have enough flow...cyanobacteria, dinoflagellates, diatoms, all these will get a better foot hold in low flow areas, sometimes just redirecting a powerhead to the area will take care of the problem.
That's all I can think of now, I'm sure others will have some suggestions. HTH