I think that the reason people say to tackle the source is because cyno CAN be an indicator of other problems. But, if everything else is good, there's no reason not to use medicine. I've had outbreaks before and the medicine takes care of it. You do have to be aware, however, that cyno is a bacteria, not an algae, so chemi clean is putting antibiotics in your tank. These can kill the beneficial bacteria as well, so you have to follow the directions to the letter. A guy I used to work with had a massive outbreak, but instead of following the directions he just dumped the container in the tank: nothing survived. If you follow directions it seems to work very well, I use it maybe once a year if I have an outbreak.