I know a few people who are so anti-chemical in their reefs buuuut chemiclean is a very safe product as long as you follow the directions to a T. air stone, duration, water change amount. I had cyano in 2 of my tanks (one of them was 3 months old when I ran it) and I also treated my brothers reef. Its safe for all fish/inverts/corals (as long as the directions are followed).
I believe cyano thrives in low/no nutrient tanks; why most people report that after using nopox or vibrant, they get cyano.
Good luck
if you do the few days without light, it may be advantageous to dim the lights down the first few days theyre back on. Im not sure what corals you have but if you want to be on the safe side, its a good practice