Here is a old post on this topic:
https://forums.saltwaterfish.com/t/255585/do-you-have-hair-algae
Do you have hair algae?
If you have a hair algae problem then read my cure all. I just recently took a tank off someone's hands, a very experienced reefer too, who had a hair algae problem that they could not fix. But the fix is so easy when you understand it. This is the instructions for a established tank. If your tank is under 3 months old read below* first.
Hair algae wont grow if you don't feed it.
1. Use Ro/DI water ONLY. If your not doing this then you are making a fatal mistake.
2. Pick off the big clumps of hair. Pull the rocks out you can and pull pull pull. Dip them back in the water to get the algae to hang down. Turn off the flow for the rocks you cant remove while you pick it off. By picking off the big clumps you remove the nitrates and phosphates from the water.
3. Know why it grows. It consumes nitrates, phosphates and light. Export the nitrates and phosphates with water changes and some cheto. Rember if you test says that you have 0 Nitrates and 0 Phosphates that does not mean you don't have them. It just means that they are consumed. If you have algae growing then you have nitrates and phosphates. Yea there in there.
4. Cut back on feeding. Where do you thing those nitrates and phosphates come from. If you have any really piggy fish then you may want to move them to QT.
5. Turn down the photo period by shutting the lights off and only turn them on for 6 hours a day. Most corals can handle this for a month. Just think of it as the rainy season.
6. Get a emerald and some mexican snails. Yea the big ones. They will both eat the short stuff.
7. Time. Give it 3-4 weeks then start to turn the lights to 7, 8...more hours till your back to a normal amount of time.
Done. Now I have my nano cube filled with sand, rocks, zoos and fish because I was able to follow this plan and he was not. Which is weird since he has an awesome sps tank.
*If your tank is new that is less than 3 months old then the question is not how to get rid of them but understanding that this is only part of the natural cycle of a new tank. If this happened just as your ammonia and nitrites test at 0 then its going to grow. Its the same reason because there is alot of nitrate and phosphate in the water. This would be the time to do your first water change and then add your clean up crew. They will take care of the algae along with water changes.
Remember don.t feed your nuisance algae and it wont grow.
Good Luck.
