1. Increase light: Koi has strong ornamental value, and many breeders will keep them indoors, but if they can't receive sunlight for a long time, their body color will gradually become lighter. Therefore, it is necessary to provide them with sufficient light when raising koi fish. If the fish tank can be moved, it is recommended to transfer the fish tank to a place with sunlight. If it can't be transferred, you can install fish tank lights and turn them on for 3-5 hours every day, which can also increase the body color of koi.

2. Feeding color-enhancing feed: Koi does not produce pigment by itself, so they need to rely on acquired food to synthesize pigment. Breeders need to regularly feed them with some color-enhancing feed to help them synthesize pigments and make their body color brighter.

3. Control PH value: PH value also has a great influence on the body color of koi. If PH value is not suitable for the survival of koi, their body color will also change. Therefore, the PH value can be controlled between 7.0 and 7.2 when feeding at ordinary times.

If koi fades, it can basically recover as long as it is not caused by dyeing. First of all, it should be rested. During the resting period, the water temperature should be gradually raised to keep a high temperature, and at the same time, sufficient oxygen should be provided. It should be illuminated with lights for a period of time every day, so that its color will become bright again.