Hello, Green Hair Algae require not only light, but also nitrates and phosphates in order to survive.
I would test your water for nitrates and phosphates.
Since you have green hair algae, your Phosphate levels should read well above .05 mg/L.The most common source of phosphates in an aquarium is from the FW used for top offs and water changes.In this case, doing water changes to reduce phosphates will only continue the problem unless the water source is changed.
Ways to reduce Phosphates:
- Use only RO or RO/DI water
- Purchase and use a good nitrate sponge. Many of the nitrate absorbing materials also absorb phosphates.
- Use Mangrove Plants in your system to reduce phosphates
Nitrates will always be something to contend with in your tank. For fast, immediate reduction, you can do a water change.
Ways to reduce Nitrates:
- Use only RO or RO/DI water
- Purchase and use Mangrove Plants in your tank or sump
- Check to see if your commercial sea salts contain high levels of ammonia/nitrogen
- Do not overfeed your tank
- Perform periodic water changes
By reducing the nitrate and phosphate levels in your tank, you will soon be healthy and free of the Green Hair Algae. Many of your tank occupants (corals and other invertebrates) will also benefit from the reduced levels.
Hope this helped,
Ben