Pay attention to frequency first when changing water for fish tank. You can't change water too frequently, but you can't be too lazy. Frequent water change will cause fish to be stimulated by new water, which will affect their health. Long-term non-water change will also lead to aging of water quality and gradual accumulation of harmful substances, which is also very unfavorable to the health of fish. Usually, it takes five to seven days to change water, that is to say, if the water quality deteriorates rapidly, it will be changed in five or even three days, and if the water quality is maintained well, it can be changed once a week or two.

Pay attention to water quantity as well as frequency when changing water. The amount of water exchanged is usually one-fourth or one-fifth of the total amount, and the maximum amount cannot exceed one-third. In addition, there is a certain relationship between the amount of water and the frequency of water change. If the water change is frequent, the amount of water change should be less each time. If the water change cycle is long, more water change should be changed each time, so as to maintain the water quality.

In order to ensure the health of fish, the temperature must be controlled when changing water to avoid large fluctuations, and the water temperature should not change more than 2 ℃. Usually, before changing water, measure the water temperature in the fish tank, and then add cold water or hot water to the new water according to this water temperature, so as to control the water temperature, so that the fish can adapt better and avoid stress reaction.