It is ok for koi to change water once a month, as long as the fish tank is large enough and the number of fish raised is relatively small. Usually, the water for fish farming should be changed once a week. If the water is not changed for a long time, the water quality will deteriorate, which is harmful to the health of fish. Each water change usually does not exceed one third of the total water volume. If you change too much water, it will also stimulate the fish. In addition, the water must be trapped before changing water, so that the residual chlorine in the water can volatilize.

1. Trapping water in advance: Before changing water, water should be trapped first. The way to trap water is very simple, that is, put the water in the sun and volatilize chlorine through the sun. This process takes one to three days. In case of rainy days, chlorine can also be removed by aeration, but a special oxygen pump is needed.

2. Pumping and water injection: After chlorine removal from new water, water can be changed. First, pump out some old water in the tank, about a quarter, preferably from the bottom of the tank, so that you can clean up dirty things such as residual bait and feces. Then add fresh water from the wall of the fish tank, and add it slowly to avoid fluctuations in water quality and temperature.

3. Precautions: The most important thing in changing water is that the water temperature cannot be changed, at least not too much. Therefore, it is necessary to measure the temperature before changing water, and then prepare new water. If the temperature difference between the two is too large, the fluctuation of water temperature will also stimulate the fish and cause it to lie prone.