Originally Posted by dnsfpl
what are these algae? what causes them?
what is the best way to resolve this issue?
We need more information (or a photograph). There are many types of algae, and each one can be caused by something different.
In general, algae is caused by an imbalance of (one or a combination of) light, CO2 and/or nutrients.
Fixing the imbalance will get rid of the algae.