koi fish. koi fish is a species of freshwater fish, koi fish live in the crystal clear waters. koi fish including ornamental fish are widely kept as a fish that has a high value. color of koi fish are very diverse kinds. water quality standards for the maintenance of koi fish is temperature 20-25 degrees Celsius. 7-8 pH, dissolved oxygen is greater than 5 mg / liter, NH3 less than 0.02 mg / liter, turbidity 40-60 cm, carbon dioxide 2-11 mg / liter, less than 0.05 ppm nitrite, alkalinity greater of 20 mg / liter, total hardness greater than 20 mg / liter.