I'd say that your environment and watering. are the two biggest things you need to concentrate on and try to master. The environment is the proper humidity, temperature and light exposure for your girl's particular time/stage of life. Feeding is important, but if the other things are not right, she's not going to eat right.
Keep things simple. You don't need a bunch of different amendments or different chemical fertilizers to grow very good canna. Master the basics, then do our own thing and make improvements.
Food. Dunno if you want to go organic, but for an easy grow, go big pots for an easier grow....more food in the bank. Build A Soil has some great soil mixes to choose from outta the bag. You could order
three things from them and have an outstanding grow............Their 3.0 mix, Build a flower, and a smaller bag of their light mix to put in the center if you direct plant your seeds. 3.0 is a little hot to germ seeds. That's it.
If you don't want to grow organic, get a good base soil mix, I like Roots Organic Original, and a bag of Mega Crop single. I used
pop22 low dose every watering method with MC and I had a killer first grow. You'll need ppm meter and good pH pen, but not that expensive.
There's a lot to learn. That's why keeping it simple is the best and learn to use LITFA when needed............
Leave It The F*ck Alone.
The most important thing...........
Have Fun in growing your canna!