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905-715-2447 Summer Hours: Open Wednesday to Saturday 10:00 am - 5:oo pm 3301 Sideroad 10, Bradford, ON Canada

Bringing Koi & Goldfish Indoors For Winter

Bringing Koi & Goldfish Indoors For Winter

In northern locations with extreme winters, some people opt to bring their koi indoors for the winter. Although koi and goldfish can survive harsh winter conditions, if you have relatively few koi, or if you have a large tank inside to house your fish, you might want to consider bringing your fish inside. Here are a few pointers, tips and advice.

bringing koi indoors for winter

Bringing Koi Indoors:


  • Fish are protected from extreme cold and temperature fluctuations
  • You can closely monitor water quality and fish health
  • You get a chance to inspect the fish closely while catching them from the pond
  • The fish will continue to grow during the winter
  • You get to enjoy your fish year round


  • Indoor tanks require a good deal of maintenance ie. feeding, water changes, filter cleaning etc
  • The fish are stress and could be injured from being caught – twice (fall and spring)
  • Usually requires extra equipment, pump, filter etc
  • Water quality problems  are common, especially during the first month which often lead to illness or death.
  • Koi are jumpers – you must make sure you tub is covered very well particularly for the first few weeks
  • The fish will continue to grow over the winter which isn’t good if you have limited space
  • You will most likely need to drain pond completely to catch fish

If you have weighed out the benefits and drawbacks of moving your fish indoors and want to go ahead with it, here a few pointers to follow to help make the transition a success.

Steps To Follow:

  1. If possible, set up your tank or aquarium filter in the pond and let it run for 1 month prior to bringing your fish inside. Then set it up inside when you bring your fish in. This will help to ‘cycle’ the filter and seed it with beneficial bacteria, reducing water quality problems.
  2. Set up the tank, install the filter etc & fill it with water from pond. Check all connections, tubing etc for leaks.
  3. The easiest and least stressful way to catch your fish is to drain the pond leaving just enough water for the fish to swim. Catch the fish, gently place them in bags or containers and bring them into the house. If you have just filled the tub with pond water, there is no need to float the bag to acclimatize the fish, just gently release them. If the tub has been set up and running for a few days float the fish in the bags to let the temperatures equilibrate.
  4. Once all the fish are in the new tub, make sure it is covered very well. Koi are very good jumpers and will jump, especially for the first few weeks.
  5. Add Beneficial Bacteria such as Microbe Lift PL , Nite Out II or Aquscape Dry Bacteria to help seed filters and improve water quality.
  6. Feed sparingly with a quality Fish Food for the first few weeks, this will help to reduce ammonia and nitrite spikes in the water. Some people prefer to feed a Spring & Fall wheat germ food because it is very digestible and the fish produce less waste.
  7. CHECK WATER QUALITY with a Test Kit. I can’t stress this point enough. At the very least, test for pH, ammonia, nitrite. Most fish illness and deaths occur in the first month, and it is almost always as a result of poor water. Filters take time to become fully active or ‘cycled’ with the beneficial bacteria to be able to properly break down the fish waste. Until the filter is cycled, ammonia and nitrite can rise to toxic levels which are very dangerous to fish.
  8. Make sure to perform partial water changes regularly. This does not mean ‘filling the tank’ when the water level drops from evaporation. You should drain 10% -20% of the water and replace it every 1 to 2 weeks (remember to add dechlorinator).  You may need to increase the frequency and the volume during the first month if you have high ammonia or nitrites, or if you have a high fish load.
  9. Enjoy your fish.


Returning The Koi To The Pond

Returning the fish to the pond is usually much easier. Just follow the steps above, but apply them to the pond. There are just a few things to consider when moving them back outside.

Steps To Follow:

  1. Clean the pond, remove any sludge and debris that has accumulated over the winter, perform a partial water change and install pumps, filters etc.
  2. Make sure your pond is running at least a week before  putting your fish back in the pond.
  3. Don’t move them outside too early. Make sure the pond has warmed up and is less than 10°F  cooler than the inside tank. Too sudden a drop in temperature is stressful on the fish and can trigger parasite outbreaks.
  4. Once the fish are in the pond, monitor them for signs of stress and check water quality.
  5. Feed the fish a proper diet according to the water temperature.