this is a common problem if you have enough light source... and enough nutrients in the water...
the easiest way to clear this up is using ocean free green away. However, the dosage on the instruction doesn't seems to be enough.... i doubled it before it clears away the algae...
of course, if you prefer to use the non medication method, there is a couple you can try.....
1) black out for a week. using only room lights.... that means you have to stick dark paper around the tank where light source are coming from and leave only the front.
2) Use barley extract in your filter. barley extract in the water will compete with the algae for nutrients.. and the algae will be drain off. however, this method is not very fast, especially if you are using those filter media type.
3) you can do a large amount of WC... however, i feel that this is not a long term plan as my green algae comes back about a week or so...
do note that green algae is actually good for your tank. it sucks up extra nitrate, and ammonia as well. it keeps the water oxygenated if there is enough light....
this kind of water is especially good for goldfish apparently....
