Im not entirely sure that is algae. Your tank looks very new, going by the bright coloring of that rock. Assuming that it is not new, and is fully cycled, you might be seeing the very beginnings of green coralline algae. I say this because algae would likely be larger patches rather than many tiny ones. Scrape it with your fingers, and figure if it is actually algae.
What to do. If it is coralline, do nothing, its a good thing, and not a problem. You will get some in pink and purple eventually also. If if is algae, then do what you should be doing already. Check your filtration, check your water parameters. Make sure your phosphates are not high. Are you using RO
. If not, you really should because it helps reduce nutrients in your water. Are you doing regular water changes. Algae is easy to correct, just start doing all the things you have learned to do to ensure good water in the tank.