Canna Rhizotonic would be fine if you dont use Advanced Nutrients, because it rises PH at the beginning. If you add acids to get PH down, then it could be just fine. See reviews around, no bad word. Comparing to Hesi Root Complex it works miracolous.
My first coco plant is 20 days old and is looking fine. I use basic nutrients and calmag and will see how they do the job before starting to play with snake oils. I do not know how it would be with root additives, but roots had reached the bottom of 15 l airpot in two weeks or even before. I think I will try voodoo juice from AN next time, but will compare different plants with or without it too see how much it adds, if at all.
Which nutrients are you going to use?
And Good luck!