I'm a huge proponent of diatom filters. I have one I got for ~$100 (can't remember the make off the top of my head, maybe Vortex XL?), and while expensive is a multi-use and very efficient piece of hardware. The benefit of a diatom vs. blackout/UV is that it physically removes the algae from the tank, so there is no worry of ammonia issues that can occur during a blackout if the GW is bad enough.
It's multi-use comes from things like parasite/bacterial disease in a tank which it can filter out during medication treatment (whereas a UV sterilizer will also likely made any water-based treatment ineffective), or when stirring up a lot of crud from a renovation.
To be honest, I haven't used mine in nearly a year because I haven't had any issues that would benefit from it (filter floss in my filter cleared up a lot of the problems), but it's nice to know it is always there if needed.
A natural remedy that I've never tried but heard great things about is daphnia. These readily feed on the GW and will clear up your problem in no time, however, you need to keep them separated from the fish since the fish will eat them (so a mesh bag/etc. needs to be used). You can then let the daphnia go and give your fish a very nutritious snack.
Here's a couple pics from a long time ago:
Before diatom filter:
After diatom filter (~45min later):
Diatom filter after removing GW: