The water temperature in the koi fish tank should be kept between 20 and 25 degrees Celsius, which is the optimal temperature range for the growth of koi fish. Within this temperature range, koi fish have better feeding and digestion abilities, and their growth rate will also increase. If the water temperature drops below 15 degrees Celsius, it is recommended to reduce the amount of feeding to avoid indigestion. When the water temperature falls below 5 degrees Celsius, feeding should be stopped.
To maintain a suitable water temperature, you can use heating rods or cooling equipment to adjust the water temperature. In summer, you can lower the temperature by shortening the interval between water changes. In winter, heating rods can be used to raise the water temperature. Besides, when changing the water, pay attention that the temperature difference should not exceed 3 degrees Celsius to avoid causing stress reactions to the koi fish.
To ensure the healthy growth of koi fish, in addition to controlling the water temperature, attention should also be paid to the management of water quality. The water quality should remain colorless and transparent or be in light green, light yellow or oily green. The oxygen content in the water should be controlled at 5 - 7 milligrams per liter. The water should have relatively low hardness and be slightly alkaline (with a pH value between 6 and 8.5).