Cyano growth can be a side effect of carbon dosing in some cases. I'd have to go find some references on the specific process, but it's something along the lines of cyano having the ability to use a carbon source when many/most other types of bacteria and algaes have become nutrient limited (That's IIRC off the top of my head, don't quote me exactly).
There is also some thinking that different carbon sources are more or less friendly to cyano, for example a lot of people have found that vodka seems to encourage cyano more than an equivelent dose (8X) of vinegar.
IME when I tried bio-pellets they seemed to feed cyano like crazy. I switched to vinegar and the cyano almost completely died out, but then over time as I ramped up the dose the cyano recovered to some extent. My best guess at the moment is that the goal is to find a dose that's just enough to keep the nutrients down, but not in excess of that because the excess seems to encourage cyano. Last I checked I was getting nitrate undetectable and phosphate @.01, then I cut the vinegar dose back about %20 and the nitrate and phosphate levels did not appear to climb but I did see a reduction in cyano.
