Originally posted by Erik
I have a ton of green algae and I'm not sure how to get rid of it. I use RO water on water changes and this white floss stuff I put into my hang on that is supposed to help.

What is the consistency of the algae? Is it slimy with bubbles in it, green water, or hairy/fuzzy stuff sticking to the rocks?

Nearly all green marine algae is caused by high nitrates (from fish waste and not enough water changes), high phosphates (from bad RO water), and high lighting. If your tank is exposed to direct sunlight at any point in the day, you'll get green algae.

Solutions (from easiest to hardest)
- Have your tank water tested for PO4 and NO3 by a pet store. They should both be at near-zero levels.
- Shade the tank from sunlight, reduce any lighting on the tank.
- Do a 25-50% waterchange every week until it calms down. Get rid of the dirty filter floss.
- Get a good macroalgae, like Chaeto or Caulerpa, they compete with the bad algae for food and are easier to clean up.
- Buy a cleanup crew. Snails (like turbo and cerrith) and Crabs (like hermit, blue stripe, and sallylightfoot) CHOW on algae. Up to one critter per gallon if you can afford it, but 10 snail + 2 crab is a bare minimum.
- Buy a lawnmower blenny or yellow tang... but this can be a bad idea for various reasons.
- Make a deep-sand bed. About 4" of aragonite is perfect. Washed playground sand from home depot is ok if you can't afford aragonite.
- Invest in a $300 protein skimmer. Don't buy anything cheap, its all or nothing. Aqua-C Remora is my favorite.

Anyways, let me know what kind of green algae you got and I can be more specific. A pic would be easiest.