Would a person put a unit (question on which one) on a pool if it was already filled? or would one just add some structured water? I remember you saying in sun it starts to turn back in 7-10 days, so in my thinking it seems it would be best on a pool if the structured water keeps going through the water structuring device. What would be the best way?

Use a unit that is in line with the pump insuring constant maximum structuring and oxygenation of the water.