how early and what strength do you use canna at for the auto flowering plants?
For I start to use nurients for any plant after the seedling stage which personally I think after 4-5 nodes or sets of leaves. I start by giving it half solution and then the next one full strengh. Some strains are more sensitive than other so you adjust from after administering full strengh to see if the plant can handle it. I would also only give nutrients on every second or 3rd watering whatever I feel at the time, then near the end of the veg stage I give it on every watering. Then I flush using rinse agent and then start the flowering nutrients doin the same technique/pattern as giving nutrients in veg but, in the middle of flowering I give nutrients every water til the end.
Pretty much what I suggest to you is that in the beginning whatever nutrients you are giving(canna, bio bizz, etc...) start with half the sufggested doseage then give it full next time so it adjusts to what your giving it, I think. after that you can start to develop doing your own techniques and when to administer nutrients and whatnot, because all plants are different.
I don't know if this helps you or answers your question. I'm sorry if it didn't. I am not a pro/expert but I can give you my personal opinion and what has worked for me. Some questions I can answer with alot of info and some I can't yet or just can't.