I'm sucking knowlege out of the depths of my brain here, so if I'm wrong, someone correct me.
Cyanobacteria, like diatoms kinda, can grow even in low light conditions. Cyano
has little protein reactors in it that turn just a little light into the energy it needs to grow and thrive. So, I don't think reducing your lighting alone will help.
Something else to try would be some sort of phosphate reducing media that you can insert into your filter if you run one.
Otherwise, I'd keep up with the limited light cycle and more water flow approach. Good luck!
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