Scrub away and water changes. I'm battling the same problem and it is all you can do. This one is actually mild compared to when I started battling mine. Cutting back on feeding is one of the biggest things. I feed my corals all kinds of different foods which ignited the issue. I actually had 8 inch long algae coming off my hob
filter (which is there because the algae plugged up my overflow so badly I had to take the sump offline) and protein skimmer, which also got clogged. Cutting back on the feeding, manual removal of the algae, water changes, and using GFO
has halted the algae's progression and I have begun to make headway.
Unhook the sump if possible and scrub the entire thing down. If not, atleast turn off the pumps and scrub it. Do a water change via the sump and turn the pumps back on.