The general water - conditioning time for raising koi fish is 2 - 3 days. The purpose of water - conditioning is to let the chlorine in tap water volatilize, ensuring the safety of the water quality. The specific time can be adjusted according to the size of the fish tank, the strength of the filtration system, as well as the types and quantity of the fish. Generally, it can be completed within 2 - 7 days.
Moreover, the water - conditioning time is not the longer the better. If the water is conditioned for more than 3 days, or even 5 days, the oxygen content in the water will drop sharply, turning the water into stagnant and waste water. Water without oxygen cannot be poured into the fish tank. Therefore, it is best to condition the water one or two days before changing the water.