Hi,
Algae is usually a result of stagnant traces of ammonia (undetectable by the standard hobby test kit) in some areas of your tank, and can usually be improved by reducing your photo-period, increasing the over all water flow and filter turn over of the tank. As Ianho has suggested, posting pictures would be helpful, my suspicion is Black Brush Algae, which is usually a result of the above conditions I have stated.
It is always better to kill the cause than keep clearing the algae, it will prevent different species from taking over the tank also.
Thanks, Jack