Your parameters are off. You killed off your biome with chemiclean and now you think a bandaid approach with a blackout will cure the problem? I guarantee couple days after the lights come back on the situation develops again. Hanna test error ratio of .03 so if you use Hanna you could be at .01. Bottomed out nutrients are the typical side effect of chemiclean which then results in dinos. Cyano is primarily controlled with flow and lights. If you do not get parameters in good stable ranges then ugly phases will continue especially since you set your biome back with the chemiclean treatment.I imagine there must be some PO4 as I have run multiple tests and 0.04 is the lowest I have had and with current fish stock and filtration I would be amazed to drop PO4 to 0. I had to sort the cyno out at it had already smothered my zoas to death, some mushrooms, a frogspawn and a hammer just about saved the candy canes. The thing is to tackle what I currently in the tank which I still don’t no. Dinos, diatoms, hair algae? Clean up grew can get rid of diatoms, dinos I need to do a black out, hair algae manual removal and clean up crew if it’s cyno I’m at a loss as I have done everything that should kill cyno.