Underwater Lighting

We recently received this question:

We are building a Koi pond and wonder if underwater lighting might be harmful to the fish. Do Koi fall into a sleep like state at night? Would night lighting disturb their needed rest time? Might the light harm their eyes? I hope you can help us with these questions.

Our Response:

Underwater lighting is fine as long as your Koi pond is deep enough - 3-4 ft. As far as falling into a sleep state at night, I have never seen that happen but there may be a slowed metabolism state at night just as they do for the winter. Night lighting won’t disturb their sleep time, it will just make them better bug hunters. The light has never been reported to harm their vision but if you are concerned as I would also be, I would just put a timer on the underwater night lights and let them go off say at around your bed time. Raccoons are night hunters and leaving your lights on may make hunting easier for them. I have never chosen to put night underwater lights in my pond but many of our members have them set on timers. You have asked an excellent question and I hope that my suggestion of a timer will solve all your concerns. Thanks for writing us and please write again if you need to.

P.S. The depth of your pond should always be a consideration when you want Koi. I don’t know the wattage of underwater lights but the heat may be something of a concern for your fish as well. In Texas, I wouldn’t add lights because our ponds run pretty hot in the summers already and heat can take far too much oxygen out of the water at night along with the photosynthesis taking place from plants. The hotter the water, the less oxygen it holds. In Oregon you may not have to worry about that as much. Check with your local pond club or organization and see what they think. Cheers and happy ponding.