Do the following...
Manually clean out as much algea as possible + 50% water change (depending on how over-run you are, you might be able to do less)
Turn out the lights, and stop any light getting into the tank. Leave the tank for 5 days in this state. Dont peek, just be patient.
When you unveil the tank again, do another manual clean of anything left (should be nothing really) and another water change.
Your tank will now be algea clear. Your plants might look a bit lean for a few days afterwards, but will pick up again soon enough!
This gives you a nice clean slate to work with, and totally nailed the algea problem in my tank.