I don't think my siphon is strong enough to do that lol but I'll try my best in a few days when I do my next water changeDon't feel bad, green or black algae are a natural thing and normal in small amounts in healthy tanks. If anything the back or sides are a great place for it, and you have a living, natural backdrop. Cyanobacteria on the other hand... I wouldn't remove the real algae from the back, just siphon the BGA off the glass to keep it in check.
Side note: does anyone know of any cool things you can feed bettas/ADF? I feel like it'd be cool to make a video of feeding Reggie/Eddie different types of bugs or chopped up shrimp or chopped earthworms and anything else that's cool (but only meats because they are both carnivores). I have a lot of time on my hands to scrounge up some cool foods so why not