Green Hair algae....
Phosphates, and or nitrates. Time to clean that skimmer out for sure! Any and all sponges on your system need to be removed and rinsed weekly.
The best method for removing hair algae (IMO
) is to take a bowl of SW
have it sitting next to the tank, reach in and pluck the algae off the rock and dip your hand in the bowl. Pluck, dip, rinse repeat. Do that until you can't stand it any more and then do it again. Reducing excess nutrients in the tank will go a long way in helping with the algae.
If you haven't tested your water for phosphates now is a good time to do so. Test both the tank and your source water. If you are getting a reading of 0, try removing as much algae as you can and test again. Chances are you will see a reading of 0 because it is being used up very quickly by the hair algae.