Green hair algae

[mr.wilson]

You need to eliminate the source of the hair algae problem which is usually excess nutrients arising from one or a combination of any of the following...

1) Frozen food isn't adequately rinsed to remove phosphate.
2) Algae is allowed to die off or strands are severed.
3) Substrate needs to be vacuumed.
4) Rock needs to be sprayed with powerhead or baster to remove detritus.
5) Source water is not zero TDS (add RO/DI unit).
6) Phosphate removal system is inadequate (add iron-based binder).
7) Not enough carbon used or allowing it to stay in the tank too long.
8) Over-feeding.
9) Not enough reef janitors (herbivores & detrivores).
10) Inadequate protein skimming.
11) Inadequate refugium nutrient export.
12) Not enough water changes.
13) Inadequate mechanical filtration.
14) Over-active biological filtration (remove wet/dry filtration if you have it).

After you have found and eliminated the sources, you can raise the magnesium (K level) in your tank to 1500 and the algae will die off in less than a month. If you don't keep on it, it will come back.