Have you read the pinned algae article?
Algae is caused by an inbalance in light/nutrients/plant growth. Algae's worst enemy is lots of plant growth. The key is to provide the ideal conditions for this growth by providing an ideal balance of light, CO2, nutrients and planting density (bio-mass). You will be getting algae because one or more of these components is off balance.
If I remember rightly you are running a lot of light - 4.5 WPG? I would suggest this is the main cause of your problem. Get your CO2 at a stable 30ppm and ensure your other nutrients are dosed appropiately. Read the lighting, CO2 and zig's Estimative Index Article for more info.
Are you planted heavily with fast growers i.e. over 50% of the substrate covered?
All the above is covered in detail in the pinned threads. Please read through them and if there's anything you don't understand then please ask.