I would take a paper towel and scoop that stuff out, as you say it is blocking light. It happens because there is very low water flow over the top of your algae wad.
If you put a little powerhead in the corner of your refugium and point it across the top of the water that shouldn't happen so much.
Looks about the same as yours. Just prune it back once in a while and it will be fine. That pic was taken after I pruned 2 - 5g salt buckets out of mine!