How much is he being fed each time? If he isn't getting bloated and eats all the food, it's ok.
But that also means you need to change the water out 50% 2x a week. Which, you should be doing anyway. The Koi needs to find a pond and the other two need a 55 or larger.
Filter should always be on.
Water looks like the tank is cycling again, so small daily water changes are needed. You also need an API Master test kit to find out when the cycle is done and you can go back to 50% weekly changes.
But that also means you need to change the water out 50% 2x a week. Which, you should be doing anyway. The Koi needs to find a pond and the other two need a 55 or larger.
Filter should always be on.
Water looks like the tank is cycling again, so small daily water changes are needed. You also need an API Master test kit to find out when the cycle is done and you can go back to 50% weekly changes.