That's a lot of hair algae! My advice is...
1. Manually remove as much as you can.
2. Add more hermit crabs and snails. (Current list of CUC possibly?)
3. 20% water change weekly.
4. Re-arrange the rocks so the algae covered side is in the dark. It should die off rapidly.
5. If the tank was used when you got it. Make sure the lights have been changed recently. When bulbs get older algae really takes off. But if they're only 6 months old they should have another 4-6 more good months.
6. Take some water to your LFS
and have them test it. You may be doing it wrong if you have had this algae for that long. You could have a chemical imbalance that could be cured by dosing.
Hopefully that helps!