I recently wanted to move some plants from my 5gal, which had some nasty algae (all sorts), that I didn't want to transfer into a new tank. As an experiment I swapped my light out for one that seems like 1/4 as bright and dropped a few shrimp in the tank. A week+ later and those shrimp are making excellent work of the algae, nearly gone. I have a betta, too, and the only shrimp he seems to not stress out are clear (amano) or brown (my cherries are sometimes brown), however.
I didn't have much success with excel. And I did try a whole tank peroxide trick once, but didn't seem to help any. Couldn't take the plants out. My algae may have been too established.
I once heard that you can dim your light with photography gels? Not sure if that's a real thing though.