Instructions
Give the koi the most sunlight possible. Install skylights or place the pond near large windows. Provide metal halide lamps if the pond is in a basement or other area with no natural lighting.
Place the pond plants to take the best advantage of the available lighting. Provide more lighting if the koi lose their coloring. Choose plants that can grow with the amount of lighting you have.
Keep the room that the pond is in at a constant temperature. Install a heater made for aquariums into the pond if it's located in a basement or other room that is not heated. Keep a thermometer in the pond and check it regularly to make sure that the temperature is steady.
Provide more filtration for an indoor pond than you would for an outdoor one, since the outdoor breezes that would normally carry away any pond odor will not be present. Store the filtration system in another room and run the lines into the pond if the filter noise is too loud.
Change the water often to keep in control of algae and fish waste that the filter will not pick up. Change at least half of the water in a large pond every week. Change a smaller pond's water less often, but watch for algae and notice any developing odor in the pond.
Install a net around the edges of the pond to catch any fish that may jump out. Build a plastic barrier around the pond if needed to keep the fish from escaping.
How to Care for Indoor Koi Ponds
For those in colder climates, an outdoor koi pond isn't practical. An indoor koi pond, however, is an unusual enhancement for any home. Indoor ponds must be treated much differently than outdoor ponds. They need special care to overcome the obstacle of being indoors and away from direct natural light.