Winter Koi Care

by DFS-Pet-Blog on November 13, 2009

**Guest post from Heath S.**

Northern Wisconsin winters are laden with snow and normally bitterly cold. This makes keeping a koi pond  rather difficult. I have tried several ways to winter my koi fish, all met with success. Depending on the harshness of the climate you are in, following some simple guidelines will keep your koi safe and secure throughout the winter months.

There are two options: Leave the koi in the pond or move them inside.  I have done both but prefer to move them inside.

Sorry No Winter Pics.  Summer 2009 Is Easier On The Eyes.

Sorry No Winter Pics. Summer 2009 Is Easier On The Eyes.

The first year I wintered them inside. At that time not being very large, 8″ at best, it was simply using an 80-gallon bowfront aquarium that I purchased from Drs. Foster & Smith.  As the water shifted below 60 degrees, I moved them in to reduce the temperature shift.

They did very well however; bringing them inside also lengthens the growing season, as they will continue to eat as normal all winter long. It didn’t help that I fed them the growth and color enhancing pellets all winter.  By spring, most had grown an additional couple of inches. I knew then that the aquarium would not hold them the next winter.

The second year, I kept the koi outside in the pond. Most of the them were well over 15″ in length. Using electrical PVC (uv protected) and 10 mil clear plastic, I began the process of building a greenhouse like dome over the top of my pond. My wife thought I was crazy and said it would never hold. It was great. I added an energy efficient heater that was inside a protective box to keep the moisture off it.

The dome held up all winter.  The air temperatures in the dome remained above 50 degrees at night and on sunny days soared close to 80 degrees.  The water fluctuated right around 50 degrees.  I was able to feed wheat germ based food well into December.  To give you an idea of the inside temperatures we actually had frogs on the rocks Christmas Day.

A view from above.  Summer 2009

A view from above. Summer 2009

January that year was bitterly cold, dipping as low as -40 degrees. The dome remained warm but the water temperature did drop to around 45 degrees.  All feeding was stopped. I ran the filter all winter, this created an extremely easy start in the spring and it did not go through the spring green scenerio as the bacterial colony was well established. Under the dome, the pond started to come back to life months ahead of schedule. By the time I removed the dome about mid May, I was actually having to hand cut green grass and the surface of the pond was already covered in lily pads. My koi handled the winter well with no loss.

Steps to follow when leaving koi in the pond through the winter:

  • Fall cleanup is a must.  Although the fish and other inhabitants go dormant, plant matter, leaves and any buildup of waste will continue to break down.  With bacterial populations low, the risk of high ammonia can cause considerable fish loss.
  • Your pond has to be deep enough if you live in a climate that causes the water to freeze over. The use of a floating pond heater and an aerator will help keep a hole in the ice for proper gas exchange. In northern Wisconsin, I would recommend using several. This has to be monitored daily. I missed checking my pond one day and the heater had gone out the night before. It took several hours to melt a hole in the ice using hot water. Never chop a hole in the ice, koi have sensors along their lateral lines that pick up even minute vibrations. I have two koi in my pond that got close to the skimmer I was working on. I snapped a hard to fit piece in place and both fish lurched out of the water. They floated to the surface for a moment and then began to swim around. They both now have severely crooked backs. You can use a water pump to keep a hole in the ice. However, you must raise the pump close to the surface so you do not draw warmer water from the bottom of the pond. This will hyper chill the pond. I do not recommend this way of keeping a hole in the ice. Depending on the temperatures, it is easy for the pond to still freeze over completely. Remember, do not have any water motion at the bottom of the pond.
  • Pond depth is also a concern. If your pond is not at least 4 feet or more in depth, I would not recommend leaving your koi in the pond over the winter.

This year I moved my koi inside. Currently they are in a 300 gallon plastic stock tank in my basement as I construct their new indoor home. Pictures and step by step indoor pond construction in my next post.

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{ 5 comments… read them below or add one }

Jenny June 23, 2010 at 12:46 pm

Hi Heath,

Would love to see pictures of your homemade pond “greenhouse”. I’m also a northern WI ponder (Shell Lake, WI) facing my first winter with koi. I’ve already been researching the best way to overwinter my koi. I want to avoid bringing them indoors if I can simply because I’m such an animal lover, it would break my heart to coop them all up in a 300 gallon tank all winter…especially when the water temps would be warm enough indoors that they would remain active.

Mary Merlin September 13, 2010 at 9:28 am

I have baby koi in my pond 2 inches to 5. I also have 9 fish that are 10 to 15 inches. Last year I wintered my fish in the garage in a 300 gallon stock tank and did well monitering the temps, filtering and heating the tank. This year I would like to do the same except i wm wondering should I get a large inside aquairium for the babys to winter in? There are about 10. Also last year the tank was by the garage exit we used and the fish got disturbed on occasion and appeared to wake and move around. Sounds as though this isn’t a good thing after reading your wintering fish experiences. Do you have any suggestions for the babies and position of the garage tank?
Thanks Mary Merlin what about pond plants?

Evan phillips April 16, 2011 at 9:27 am

I was wondering if anyone has brought their koi in and kept them in a aluminum metal watering trough. I have three that are 160 gallons that are not being used. I live in buffalo ny and every year have had dead loses due to the winter. My outside pond is around 4000 gallons. I currently have 15, 10 to 15 inch koi in my pond. Are these metal tubs ok for them, and is that enough room for my koi? Please help

Heath S. April 21, 2011 at 2:15 pm

Evan, sorry to hear of your winter loses. If you use the metal or galvanized stock tanks, I recommend using a pond liner in the tank as well. The galvanized metal contains zinc and is toxic to fish. For years I used a 300 gallon stock tank for my koi, as they are all very large I had to perform weekly water changes, filter cleaning and reduced the amount of food to ensure the water quality. Wheat germ based food seemed to produce the least amount of odor for the indoor tank as well.

Ashley January 24, 2012 at 4:12 pm

I can’t stress the importance of the depth of your pool for keeping your koi stress free and healthy! We’ve had many customers suffer losses because of a lack of depth.

Glad to see from your next posts that the winter period went well!

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