Green Hair Algae

[BCOrchidGuy]

Mark hit upon a very good point, try to get your water parameters verified by either another hobbiest or a LFS. Test kits can go funny even if they haven't expired, stick with a quality kit, I've used SeaChem and liked them although the Mg test was mind bogglingly complex. I'm using Salifert right now and like them very much. Hagen and Tetra both gave me problems in the past and I lost my trust in them.
You've either got a nitrate problem or a phosphate problem if it's nutrient, if your light is old or running very very yellow it will be a big contributor as well.
The other thing you could do if your tank is established is to move the livestock to either another tank or to containers, mix up a 100% water change in some clean garbage cans (plastic) and then drain the aquarium and refill it, take your time getting the livestock used to the new water chemistry and then do regular weekly water changes until the GHA is allllllllllll gone.
Final tip from me, a fox face and a tang can eat a lot of algae and make the job go much quicker.

Doug