The water in the fish tank should be changed once a week, and if the water quality is maintained well, it can also be changed once every half month. Usually, the cycle of changing water is not fixed, mainly depending on how long the water body will become turbid. It is not good to change it too frequently, which will stimulate the fish. The purpose of changing water is to improve water quality. Long-term failure to change water will lead to deterioration of water body. Even if it looks clear, harmful substances will increase, which is harmful to the health of fish.

1. Raise water in advance: Before changing water for fish tank, prepare water first. Because tap water is usually used, this water contains residual chlorine, so it must be dried for one to two days, or oxygenated by an oxygen pump for a period of time before it can be used. If you don't pass through trapped water, it may do harm to the health of fish.

2. Pumping and mixing water: The method of changing water is relatively simple. First, the old water at the bottom is pumped out with a water pipe, so that the fish stool and residual bait can be cleaned up. After pumping water, slowly add new water from the tank wall. The advantage of changing water is to avoid water quality fluctuation and make fish adapt better.

3. Precautions: Usually, don't change water too frequently, and don't change it too much every time. Generally, change it once every one to two weeks, and one fifth or one quarter of it every time is enough. But also pay attention to the water temperature. The new water can be 1 ℃ higher than the old water, but the difference should not be too much.