<a href=showthread.php?s=&postid=13547452#post13547452 target=_blank>Originally posted</a> by jdieck
Your bio-load is on the high side and feeding causes your high nitrates that in turn feed that microalgae.
So You need to get those nitrates down to get rid of the algae:
a) Reduce bio-load
b) Reduce feeding amounts and/or frequency
c) Improve skimming by skimming wet or increase your skimmer capacity.
d) Install a refugium with macroalgae (Chaetomorpha) to compete for the nutrients with the microalgae and periodically harvest the algae. If properly sized try including a DSB for nitrification. Populate it with a kit of pods and bristle worms.
e) Increase the amount of live rock if it is below say, 1.5 pounds/gallon
f) May use some Nitrogenous compound removal resin (Like Purigen)
g) If you have any mechanical filters clean them frequently.
h) Use carbon also replace it more frequently
i) If you by chance use any kind of trickle filter, remove the bio-balls over the course of several weeks.
j) Use granular ferric oxide GFO (Phosar, phosban etc.) to remove phosphates (another nutrient)
k) Keep the weekly 20% water changes until nitrates start to drop
l) If your light bulbs are older than 1 year, replace them.
m) Test and keep your magnesium at 1300 ppm, your alkalinity at 10 dKh and your calcium at 420 ppm
m) Check your tap water, If it is trated with chloramines then you need a special DI cartridge right after the membrane to remove the ammonia after the carbon breaks down the chloramine. DO not worry about using Amquel, it will only remove the toxicity of the ammonia but does not take it out of the chain of nitrification.
That's all I can think to help reduce nitrates.
Good Luck!