Turbo snails, Bristletooth Tomini tang, Foxface. Our one spot Foxface rabbit fish eats the algae. The turbo snails definitely do a good job. Especially the larger ones.
Sea Hare! Just picked me up one a couple days ago and he has been munching away at my GHA. Just be ready to re-home him when he's cleaned up all your algae as they will starve without it.
Short answer. Bacteria. A product that I have been having a lot of success with is Vibrant. I used to work for a aquarium service company and I would say that I used Vibrant in about 90% of all my services. Gives a lot of stability and the bacteria competes against the algae for nutrients, reducing significantly algae issues of any kind. A plus is that its natural so you can't really overdose. Here it is https://amzn.to/3qDVyrY