most of the time an algae outbreak is due to overfeeding. i had a similar case about a month ago... but mine was more brown, anyway i cut down on my feedings (amount fed, and times fed), i also dialed in my fertilizers. my algae is 90% gone (and it was bad). only feed as much as they will in 2 mins, and i cut back to once every other day... it'll take a while to get rid of, but it will shrink back. the water change is a good way to remove a majority of any unused nutrients left over in your water, ie food or ferts the plants and fish are not consuming... just scoop as much algae out every week during your water change as you can, really monitor your feedings, and be patient.