Fish tank should be changed for tap water. The reason why we don't choose river water is that it may contain bacteria, which is particularly fatal to ornamental fish, and the temperature of well water is relatively low and dissolved oxygen is not high, so we can't raise live fish. After disinfection, tap water will do no harm, but there will be residual chlorine, which needs to be removed by trapping water to ensure that chlorine in water dissipates before it can be used to change water for fish farming.

1. Trapping water in advance: Before changing water for fish tank, 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.