Before changing water for fish, prepare new water first. The new water usually uses tap water. Although this water is not polluted, there will be a small amount of chlorine after disinfection, which is very harmful to the health of fish, so it is necessary to remove chlorine by trapping water. After connecting the water, put it in the sun to dry for about one to three days, and the chlorine gas can volatilize clean.

After fresh water is ready, you can start changing water. First, the old water in the fish tank is pumped out. If the fish tank is big, it is best to use a water pump. Small fish tanks can use a pipe to pump water artificially, that is, siphon method is used to suck out the water. After pumping out the old water, inject the new water into the fish tank slowly. Don't worry in the process, and don't change the water violently, so as not to disturb the fish.

Be sure to keep the water temperature during water change. Because fish belong to temperature-changing animals, their adaptability to temperature is poor, so the water temperature must be controlled. Usually, before changing water, measure the temperature of old water, and then mix new water according to this temperature, so that the temperature will not change during the process of changing water.

Usually, there is no fixed period for changing water, which should be decided according to the situation of fish tank and water quality. The short one should be changed every three days, and the long one can be changed every half month. Every time the water is changed, it should not be changed too much, usually not more than one third of the total water quantity, otherwise it will also cause stimulation to fish and even produce stress reaction.