[mr_alberta]

Thanh, is the algae very coarse or soft like cotton? There are a couple algaes that seems to like low nutrient systems (i.e. zeo systems).

If it is cotton like then you can try Mexican turbos as some have had success using those. If it is the coarse stuff though it may be more problematic. I've heard of some people having luck with the combo of manual removal + a sea urchin.

Regardless of what type of algae it is though, make sure you have a decent clean up crew to begin with and they should be able to help keep a lot of that stuff in check before it gets really out of hand.