Looks like your idea should work, but algae can survive with only 10-20% of the normally available light. If it doesn't work out, then maybe consider going with a wood "flume," made of cypress. Let the algea grow and simply consider it as an adjunct part of the filter system, (like the green fur algae that should never be scrubbed from the sides of a pond.)
But, as you say, so far, so good!
Mike S.
Spring Hill, FL