To answer HOW to get rid of the algae..
it looks to be hair algae, in my experience this is very hard to get rid of but It's not impossible. Cut back on lights, do water changes regularly, test your RO
water for phosphates, and cut back on feeding. Try pulling out heavily infested rock and clean off as much algae as possible with a brush. Make sure you rinse the rock before you replace it in the tank. This can help dramatically but not a guarantee to cure the problem. Clean up crew such as snails and crabs will do nothing for your problem. I had a bad algae problem 5 years ago with hair algae. I ended up taking all my rock out and scrubbing the heck out of them. Replaced the rock and did a 50% water change. This is hard on your tank but if desperate measures call for it, it works. Luck for you, it doesn't look like you have a lot of live stock. Were do you get your water? And have you tested your tanks parameters ?