The stocking density of koi fish needs to be determined according to the size of the fish tank and the size of the fish. Generally speaking, it is a relatively reasonable density to keep one centimeter of fish per liter of water. If the density exceeds this level, the deterioration rate of water quality will accelerate and the fish will also feel uncomfortable.
For example, an aquarium with dimensions of 60 cm × 30 cm × 15 cm can stock 6 koi fish with a body length ranging from 15 cm to 20 cm. An aquarium measuring 90 cm × 30 cm × 50 cm can stock 8 koi fish, while an aquarium of 110 cm × 30 cm × 50 cm can stock 10 koi fish.
The factors that affect the stocking density of koi fish include the size of the fish tank, the amount of water, water temperature, oxygenation status, as well as the size and growth condition of the fish. If the filtration system is powerful, the stocking density can be appropriately increased. On the contrary, if the filtration system is weak, the density needs to be reduced to maintain the water balance. In addition, koi fish have a relatively large appetite, so an overly high density will lead to a rapid deterioration of water quality and affect the health of the fish.
To keep the water clean and balanced, it is recommended to clean the fish tank regularly, change the water appropriately, and pay attention to observing the behavior and color changes of the fish. If it is found that the fish are showing signs of discomfort, the stocking density should be adjusted in a timely manner or other measures should be taken.