This could be due to a number of factors – poor water quality, lack of oxygen, parasites and poor nutrition. A food with a high level of stabilised Vitamin C will help build up the immune system and perk up your koi. Also, look for Vitamin E as this helps stress related problems. Soaking the pellets in orange juice will also help. Incorrect nutrition will result in unhealthy koi, regardless of how good the water quality is.
Koi for dummies – our practical guide to koi keeping
Simply written and easy to understand. Koi for Dummies is your useful guide to koi husbandry. How to get the best out of your hobby and fish!