Cyano is not an easy thing to combat. My first suggestion would have been to use RO/DI water, but you already have that. Then, I'd suggest the use of snails, but you got those as well.
Basically, I am at a loss of words. You may want to get a phosphate sponge in order to get those phosphates lower, the lower, the better.
Do you test your alkalinity, what is the reading?
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