- The koi pond should be close to your house so it's easy for you to get out twice a day to feed the fish and check the pond for problems. There shouldn't be any trees above it that drop waste into the water, and the pond should be around 6 feet deep because koi need a lot of space to thrive and somewhere to hide from predators. A deeper pond is also less susceptible to temperature changes. The pond should be away from sprinklers and sealed from the outside to prevent garden and lawn fertilizers from leaching into the water. Koi ponds can be lined with sealed cement or plastic liners. Most koi ponds do not contain any plants because these compete with the fish for oxygen and the fish tend to dig them up.
- To keep the water clean enough to see the koi and prevent disease and dangerous types of algae, a koi pond needs a bottom drain, a mechanical filter and a biological filter. The drain should be placed at the deepest point of the pond where waste naturally collects. Water from the drain travels first to the mechanical filter where solid wastes are removed and left in a settlement tank. The water then moves to a large biological filter where aerobic bacteria remove ammonia from the water before returning it to the pond. Both the settlement tank and biological filter must be outside of the pond. Koi ponds should also have a skimmer to remove surface debris.
- Koi need moving water and a lot of oxygen to be healthy. Aeration is usually provided by a waterfall that returns filtered water to the pond, increases circulation throughout the pond, and mixes oxygen into the water. A waterfall is also a good way to keep a trickle of fresh water moving into the pond because chlorine from municipal water sources is removed by the oxygen in the air as the water flows to the pond. Some koi ponds also have jets to further aerate the water and make it circulate better. Koi prefer moving water, and jets help prevent dead spots of stagnant water in the pond where ammonia and anaerobic bacteria can collect.
