Hob overflow evolved into algae scrubber?

My aqueon hob overflow is a clear acrylic that for the past 10 months has been exactly that, clear. Ive had HA grow on alot of other surfaces in tank but just recently my overflow box has been blooming with hair algae, and i can easily run a scraper through and wipe a whole side clean, so essentially is this acting as a turf scrubber now? Im afraid to wipe it all clean in the fear that it will localize itself in the DT where i dont want it. What could be the cause of the algae growth to suddenly shift to such a convenient location?