Good question. I'm kind of shooting in the dark without a lot more info.
Algae needs several things to grow. Remove all of any one thing and it dies.
It needs a place to grow. Well, that's the glass and rocks in your tank. Not much you can do about that.
It needs nitrate and phosphate. Look at fertilizer for your plants. What's in it? Nitrate and phosphate. How does it get in your tank? The most likely suspect is over feeding. Both excess food that decays in the tank and the detritus that goes from poop to ammonia to nitrite to nitrate. It has to be removed. There are other ways like rocks that leach phosphate, but that's rare.
It needs light, and specifically red or white light (white is made up of all spectrum so there is red in white light). Some reefers do all lights out for 3 days (that's about all the coral can safely tolerate). But your corals use way more blue than red. So running only the blue lights (assuming you have controllable leds or t5) for a week or more can be useful. You may have to wrap your tank in something to block outside light. But if you don't solve the fertilizer issue, when the lights go back on, the algae will start up again.
You could pull those rocks out of the tank and dip them in hydrogen peroxide (H2O2) for 3 to 5 minutes. It should (no promises) kill the algae and should not harm soft corals. You probably have to dip for only 1 or 2 minutes if you have lps or sps corals (I have no experience dipping lps or sps).
You could try Chemi-Pure or one of several other chemical treatments. But I try to hold them as a VERY last resort.
