http://www.thekrib.com/Plants/Algae/red-algae.html

seems like all algaes are a chemical imbalance between water and plants, and
even fish load....

thus the water parameters...

Some say trace elements are needed for plants to absorb all nutrients from
water... in other cases of algae, you may be missing only one and it's off
balance, and I think beard algae is that one...

CO2 means alot to getting rid of algae... i use pressurized CO2 and I've
never had an algae problem.... 2 years, *knocking on wood* and no algae,
anywhere..