What cuc do you find works for GHA?How big is the tank? Could you house a lawn mower or starry blenny? I find them to do great with different types of algae, like hair. I'm pretty sure you're dealing with the start of GHA, green hair algae, on that back wall and rock. The sea lettuce you'll probably need to manually remove and then maybe a cuc or blenny will take care of it for you.
For me GHA was all about the right cuc and fish in the tank after manual remove on my part. Yours is still pretty short, so I think a good cuc and herbivore will take care of it for the most part.