The feeding amount of 20cm koi is about 30-40. Koi is an omnivorous fish. There are many things to eat, and it eats a lot. It must be fed enough at ordinary times, otherwise it may fight. It should be noted that because it has no stomach, it is unlikely to be full when feeding, and it may eat all the time, but it is necessary to control its appetite, otherwise its excretion will increase, which will affect its water quality and threaten its health.

1. Animal feed: Animal feed mainly includes fish insects, Cyclops, water earthworms, paramecium, wigglers and so on. This kind of food can survive for a long time in the fish tank, which can stimulate Koi's interest in eating. This kind of feed also contains a lot of protein, vitamins and other nutrients, which can promote the hair color and growth of koi.

2. Plant feed: Although animal feed is the main feed for koi, there should also be a proper amount of plant feed, such as weeds and aquatic plants. This can ensure the balance of nutrition, which is beneficial to its growth, but it cannot be fed this feed for a long time.

3. Synthetic feed: Synthetic feed is rich in protein, sugar, vitamins, inorganic salts and fat, which can ensure the normal growth of koi. Eating these foods can also enhance the resistance of koi fish, so that they are not easy to get sick. Furthermore, eating this kind of food will make koi fish's hair color more uniform and make their gonads develop more soundly.