That was just my personal experience in approx. how much I might find myself using chemiclean. I use it when I get cynoalgae that has built up usually due to my own lack of maintence, like not changing out GFO regularly, water changes ect. Also People using sugar,vodka type introductions of carbon have had an onset of cyno through thier dosing. I'm certainly no authority on that subject. It is a safe product IMO when the directions are followed. I have a strictly all SPS tank and have never had any harm come to my coral from the product I use (Boyds Chemiclean) to irradicate the over growth of cynoalgae. However If you are have a problem with this type of algae there is an underlying excess nutrient issue that if not delt with will never go away. The Chemiclean is simply a tool used IMO to help clean up when an excess nutrient issue has presented itself in the form of cynoalgae. It isn't meant to be used as a sole means to keep your tank free of this problem. Hope that helps.