Found some info on this topic.
I remb asking the boss of a LFS and he told me do more water change. Bio load and nutrients are a major cause. I increase WC regiment and found e GSA growth to slow down.
What Causes Algae Overgrowth?
Like any plant life, algae thrive on three basic necessities: water, sunlight and nutrients. If an excess of any are available, algae will grow like wildfire, just like weeds growing in a garden.
Obviously you can't do without water in your aquarium, but you can control the amount of light and nutrients are in the water. Here are the common reasons for algae overgrowth.
Lights left on too long
Aquarium in a location with direct sunlight
Overfeeding the fish water changes
Using water with high nutrients
Avoiding Algae Overgrowth
Knowing the causes of algae overgrowth is the first half of the battle. Here is what you should do to avoid overgrowth.
Reduce Lighting – Don't place the tank where there is direct sunlight, for even part of the day. Sunlight can, and will, promote algae growth. When using artificial light make sure it is not stronger than necessary, and is not on more than about eight hours each day. To ensure that, use a timer to turn the lights on and off each day.
Feed Less – The majority of owners overfeed their fish, which increases the phosphate levels in the water. Feed small portions and watch the fish eat. If all the food isn't eaten in five minutes, you are feeding too much. Always remove any uneaten food promptly.
Water Changes – The single most important way to avoid algae is to perform regular water changes. Change ten to fifteen percent of your aquarium water every week to keep nutrients in the water low.
Know Your Water – Test your water source. If it is high in phosphates, you should consider using phosphate removers or find another water source. It's wise to also test for nitrates, as some water sources have elevated nitrates. It doesn't do much good to change the water if you are adding nutrients!
Clean It Up - If you see algae beginning to grow on the glass, rocks, or other hard surfaces of the tank, remove it. Scrape the glass, remove rocks and scrub them, and vacuum the gravel when you perform water changes.
Keep Live Plants – Live plants will use many of the nutrients that algae thrive upon. Fewer nutrients means there is less fuel for algae overgrowth.
Keep Algae Eating Fish – Keeping Siamese Flying Fox, Otocinclus, or even the common Plecostomus, will help reduce some of the algae in the tank.
http://freshaquarium.about.com/od/al...ttackalgae.htm