Sam, then you have never seen my tank. I have a 5,000 l/h and a 5,000-15,000l/h wavemaker, a 3,500 l/h pump with a corse filter and the canister filter that is doing over 1,000 l/h all in 430 l and I still have cyano - and lots of it.
A blackout does work well in my experience, and I think that Cyano is caused (or not helped) by too mush phosphate.