I started using it because I was getting hair algae on two rocks in my tank. The rocks were weird shapes and jutted out into the front of the tank, so it was difficult to get sufficient flow around them to keep crap from getting trapped in them.
I didn't see any difference whatsoever until the third or fourth week. Then, it seems, overnight, all the cyano and hair algae disappeared. I had to give away my sea hare to a friend because there was literally not one bit of food left in the tank.
I am still dosing weekly, but in a couple weeks will probably move to the monthly maintenance dose. It is very expensive, especially dosing 300 gallons worth weekly, but man did it do the job. I have never seen anything like that before.