Have you checked for phosphates? With that big of a WC your bound to get em. I would limit my WC to once weekly at about 25%.
Algae needs to feed and phosphates are their #1 food source. Phosphates come from a wide range of things, including uneaten foods, fish waste and tap water. Your doing right by lowering your lighting. I would also try feeding once a day or even every other day. You can also get a
phosphate remover from you
LFS.
Hope this helps, I know it did with me.
p.s. How's your
ICH outbreak? I've had it in my bio cube and just wondering what you've done to get rid of it.