I grow in Canna Coco, so I'll offer a little input on the nutes. I do seem to prefer House & Garden nutes over Canna, some may disagree. As far as Canna sucking with RO water, are you adding 5ml/gal Cal Mag first? That's what I do. I've had good results with either the H&G Cocos AB or Aqua Flakes, either works.
I recently read a thread where a guy uses nothing but GH Maxibloom (powder) for his Coco, says it works great. Maxibloom is buffered to 6.0 pH, so it's not too high (coco likes 5.8 ) and he says it just works with no hassles.
I also read from an experienced grower who has run organic soil, coco, dwc, etc... that the Bloom Advanced Floriculture Euro AB (yellow bottle nutes) give the most soil like taste results from coco. He said their Humic product is like liquid soil, supposed to be good stuff. He likes the yellow bottles better than house & garden.