NPK and aquarium water

hello. i use the old water from my aquarium to water plants around the garden and pots. this will be heavy with nitrogen which is fine over the winter months, but i would think a change to potassium levels is more desirable come spring to promote flowering. anyone know the best way to go about this? if best to leave as is, there is no waste as it will go on the bananas and/or phyllostachys. thanks