This seems extreme. If you soak and scrub the rocks, what's stopping this from happening again? You're not just disturbing the algae but also setting back growth of coralline algae, biofilms, microfauna, and any coral stuck on the rocks. All of those are what makes a "mature" system and are part of the long term solution. If the herbivores are the solution, why wait? You can always add more if you it's not keeping up. If the algae is living off of "new tank" symptoms, it will starve itself out and a more balanced ecosystem will find its place. I would only advocate doing something crazy like this to eliminate a pest algae that can't be handled easily like valonia or bryopsis. Even then, a bit extreme.
Some of the symptoms I am seeing here suggests more than an algal bloom. Zoanthids not opening up because of nutrients? I don't think so. Nutrients make corals grow faster, not slower. Only "extreme" nutrients supposedly slow their growth, but I have seen pretty extreme nutrient tanks with more healthy sticks than I could count.