If the water body is large, you can put some palm slices and attach eggs.

Koi fish should be nursed back to health in time after spawning. Take a passage from my paper for your reference:

Attention should be paid to the nursing of postpartum parent fish in koi fish;

First, male and female fish should be separated. When replacing the cage, they should be taken out together with the hairtail in the basin to avoid mechanical damage to the parent fish. For the injured parent fish, the wound should be treated: the fish body should be soaked in 1% potassium permanganate solution for 20 min, and the skin injury should be coated with sulfanilamide ointment or penicillin ointment. In severe cases, antibiotics should be injected and some health care agents should be injected.

The second is to feed suitable high-quality bait in time. Parent fish are generally weak and have poor appetite after spawning, so feeding should be reduced. Stop eating or eat less on the day of spawning. After that, according to the food intake of the parent fish, the feeding amount is110 ~115% of the usual daily feeding amount. Try to feed fresh bait or concentrate special for koi fish, and then manage according to normal feeding technology after the parent fish's physique basically returns to normal.