If koi eats the scavenger, it is best to change its water. It is normal for fish to eat each other. Usually, big fish will eat small fish. Koi is a big fish and likes to live under the water. Scavengers are also benthic fish, so it is inevitable to be eaten. However, koi carp is rough when eating, which may lead to scavenger's bodies everywhere, which will damage the water environment, so it is necessary to change the water properly.

1. Similar body shape: First of all, we should pay attention to the body shape of fish in polyculture. It is less difficult to mix fish with similar size, because they are similar, so they don't want to eat each other. As long as they are gentle and not easy to fight, it is safer to mix fish. If you bite every day, it will also cause certain losses.

2. Similar habits: Fish raised together should have similar habits. For example, their requirements for water temperature and ph, if they are all fish that like weak acidic or weak alkaline water quality, it is more convenient to adjust the water quality. If one likes weak acidity and the other likes weak alkalinity, no matter how to adjust, one party will always be unable to raise the state.

3. The fish tank should be large: In order to ensure that the fish will not fight when they are mixed, they must prepare enough space for activities, otherwise some fish have territorial awareness, especially during estrus, and it is easy to fight if they are too crowded.