Criminal

Bit small for 3 weeks growth. You’ve overpotted. Seedlings should be started in keg cups that way you can water every day and increase oxygen to the root zone which makes for explosive growth. They look healthy but next time use a much smaller pot.

The leaves are dying because Canna AB are too low in nitrogen. They’re not suitable for veg. You also should never water coco with just plain water. It strips the cation bank which is making the lack of nitrogen even worse. Just a few tips.