A little trick for cleaning this crap.
1 I use a small dia hose abot 3/8".
2 At one end attache a nylon stocking that is doubled and I set this in the sump(preferably attache to the edge).
3 Then start a siphon and using your finger near the tip let the algae pull into the tube then block siphon with finger, thus trapping the algae and pull(gently) away from the surface.
4 Remove finger suction starts up again and away it goes.

I find it works great, let me know......