Hello Ozzy, your plants don't get enough light. looks like plant on the right gets most of the lumen, this is why it has bigger flowers. The plant on the left is stretching up in search of more light. Swap the places of the plants and if you will see more improvement (on the left plant) and reduced progress (on the right plant) that would prove my theory. How ever I am quiet sure, this is the problem, as other than that they look healthy, but slightly over fertilised. Some one might advice you to decrease nitrogen and increase PK but I don't think this is the case, because canna coco is a reliable nutrients and on the top of that you are using PK.