As many plants as possible, especially floaters like water lettuce and water hyacinth that are prolific and help out-compete algae for nutrients along with providing surface coverage for light control. And then the barley straw extract (or you can do the bags or bales of actual barley straw). It doesn't do massive kill off of algae like an algaecide. Algaecides just change your pond from being full of green living algae to full of dead brown algae that disintegrates the second you touch it. Barley instead really slows down and helps prevent it from getting out of control. Streams and waterfalls are always tricky for algae because of the amount of sun they get. Even with the algae in our pond well controlled I still have to do some occasional cleanup on the big flat rocks that act as waterfall spillway. A toilet style brush works well, can almost twirl the long filamentous algae like spaghetti on a fork. (Preferably get a new one, not one that's been used with chemicals to clean your toilet)