Your PH is much too low for soil growing. You need to be looking for a ph around 6.3 - 6.8 for your in-going water.

Did you really mean to type 40mls of Rhizotonic? Following the Canna feed schedule it should be more 10 - 20 mls into 10L of water for the veg stage.

200mls in a 5L pot isn't really all that much imho. I use 4.5 L pots for my young ones in veg and give them appox 500mls each depending on their size. I water them slowly letting it soak in until there's a bit of run off and the pot feels nice and heavy. Next watering is when the pot feels light again.

5L pots are also pretty small for going right through to the finish of flowering - what strain of plants do you have there?
If it was me with 30 plants I'd be considering a sprinkle of dolomite lime to each pot and watering in, then potting up to a 12L with quality fresh soil. I'd ease off on the feeding until their ph is in a range that the plants can utilise it properly and then start again lightly.

If you can photo's would be good and also filling out the trouble shooting form - its a sticky at the top of the page. That gives people a much better clearer idea of whats going on and how to help.
All the best.