Great to hear that the plants are looking / growing better again.

May I ask, at what time of the day do you water? For info, I water when it's the "morning", so that the plants have the whole "day" to drink before going to bed happy and satisfied.

The weird spots - you have 12 plants in 3 gal pots in 10 square feet of space - with the amount of water given to the plants I would monitor the humidity of you grow room first to establish if this is the cause of the prob. Don't be disheartened though, it takes a little time for plants to respond to increased / decreased anything. I know you have a dehumidifier - have you any way of testing that it if dunctioning correctly?

Do you rotate the plants? I rotate and re-position constantly, so they all get equal time in various positions. Helps with grow room hot spots, incomming cold air, etc, etc.

Not too sure about the new growth being more yellow than it should be. I'm not familiar with the Canna Bio products, but rather than overnute, there may be an instance of something lacking. Give them a few more days, then compare.

It's not really possible to say accurately when they will need watering again - the plants will let you know when they need water.

Hope things continue to improve.