Hust to clarify, cyano is a type of photosynthetic bacteria. That is the justification for using a bacteriacide to control it. I've never tried it and can't give any advice on its effectiveness, one way or the other. I do share the concern that it would have a detrimental effect on other beneficial bacteria in a system.

I do feel that phosphate is the ultimate cause of any pest algae bloom but as was stated there is no accurate way to measure it, at least on the hobbyist level. From what I have read and experienced, I think that the additional current doesn't necessarily provide direct control of cyano. Rather, it limits the amount of organic detritus accumulation that the cyano seem to thrive on. The worst case of cyano I have seen was in my own FO tank that was beeing fed heavily and had a minimum amount of circulation.

Gary