Can't get rid of Hair Algea

[newsalt]

I have had a hair algea issue for several months. No matter what I do, it won't go away. I've check several forums on the topic and they all go over the same things:

Do you use RO/DI water?: Yes, my RO/DI TDS is 000.
How often do you feed?: Practically never. Like once a week.
Do you use PO4 remover: Yes
Do you have a clean-up crew?: Yes, hermits, emeralds, turbos, nerites, & astrea
Are you Skimming?: Yes. I have an MRC MR-2 skimmer cleaned approx. once a week.
Do you have a fuge?: Yes. I have calurpa and cheato in there on a reverse lighting schedule.
Have you tried turning the lights off for a few days?: Yes

I siphon out softball size quanities of HA during water changes, but it doesn't go away.

What can I do?

[Davidb6]

What is your Magnesium level? Also, check your silica level.
Increasing mag will get rid of the hair algae...just do it slowly and watch your tank.

I see you have MH, do you have SPS? If so do you add anything at all to the tank?

[demonsp]

Whats used for flow?
Age of tank?
Water change scedule and amount?

[newsalt]

Water Params:
pH: 8.26
PO4: 0.05 (Hanna)
Ca: 425
Alk: 10.6 dKH
Mg: 1440

Tank is 1.5 years old. For flow I have one Maxi-Jet 1200 mod, a Maxi-Jet 1200, a Maxi-Jet 900 and whatever my return pump produces. My water change schedule is 20g per month.

[Patrick12]

I too would recommend the increased Mg level. You can safely go up to 1500 ppm. I had to do the same thing and it worked for me. My water was perfect ...even the silica and iodine. My Mg level was about 1250ppm. A word of caution though, I would not raise it more than 100ppm a day. There can be impurities in some of the Mg salts and adding these too quickly can cause problems. Raising the Mg itself more than that is not really a problem.