Wintering Your Pond Fish Inside

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While many pond owners have found ways to overwinter fish in a pond all season long, others due to many factors may choose to bring their fish indoors during the winter.

As to which one is best for you will depend on a lot of factors. The type and depth of the pond you have is a major one, while your indoor digs may also be a factor. However the good news is that keeping fish indoors is neither hard or complicated to do.

In the video below we’ll talk about some important things to remember if you choose to bring your fish inside during the winter months.

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As noted, it’s important to keep good aeration and good filtration going in your indoor pond. It’s more or less a big indoor aquarium. A small pond aerator and / or a submersible pump and filter of adequate size will do the trick. If you have Koi keep in mind that they can release a lot of waste and filtration will be essential. Get more than you need in terms of capacity keeping the pond size and the fish load in mind.

As always it’s a good idea to keep an eye on ammonia levels throughout the winter just to be safe. You can do that with test strips or other measuring devices.

And finally here’s the primary thing to keep in mind while wintering fish indoors. Place them where you will not find major fluctuations in temperature. For instance I could not winter my fish in my garage since it is unheated. It may be quite warm one day and below freezing the next. A relatively stable temperature and conditions are the best way to avoid stress on the fish.

Do you have any experience or advice on keeping pond fish indoors during the winter?

Please consider sharing your comments and expertise below.

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15 thoughts on “Wintering Your Pond Fish Inside”

  1. I leave my fish in the outdoor pond which is 4′ deep. Lst year I installed a heater to help with ice buidup on the water fall. I run the fall 12 hours per day. Surface has little ice with the water movement and the heater. I also cut back my surface plants and place them in the deep water.

  2. Hi Brian,
    This is a good question and I’m not sure I have a clearcut answer for it as I have never really pushed the extremes of this. Less variation is better of course.

    Water does serve as somewhat of a buffer in terms of temp swings and even when it’s cold outside, with the use of a smaller pond heater, you can warm the water a good bit.

    Using some of the pond water itself on the indoor transfer isn’t a bad idea as the temperature shouldn’t rapidly change between the two if it’s done expediently.

    A good pond thermometer is pretty useful in cases like this since you can monitor the two ponds to see how close things are.

    Generally I would suggest if you could keep the temps between 10 degrees…you’d be doing quite well. I know for a fact that other pond owners have relocated fish in an even broader temp swing that that, but to what degree you could get away with it, I’m not certain.

    Can anyone else share some experiences here of transferring fish in a broader temperature range than what I’ve mentioned here?

  3. We have goldfish. The straight tails stay out all winter. The pond is about 3 feet deep. The filter runs all the time so if the water freezes the return area stays open. The water fall also never freezes. The fantails come in for the cold season. We just brought them in this week. We filled the laundry tub with pond water and left the fish in it for 24 to 36 hours. This brings the water and fish back up to the same temperature as our 125 gallon tank. Because of the enormous size of our 7 fantails we run triple the filtration as the tank would normally require.

  4. Hi. We live in Manitoba where it gets really frigid. In the fall, before the pond freezes, I set up my aquarium, fill with water, including some of the pond water. Not a lot but enough that the bacteria will get into the filters and the water is comfortable for the fish. I leave the aquarium run for three to four days then I collect the fish from the pond into a large pail or tub which has been filled with pond water. It is not easy to catch the fish as they hide really well. I usually have to search through all the rocks and move them all to find the fish. Then I take the tub into the house and leave it overnight. In the morning I transfer the fish into the aquarium, leave for two hours and then feed them. In the fall I do the reverse. I have never lost a fish from shock and the fish I have had for several years do not mind the handling. In fact there is such a lack of trauma that they willingly come to my hand after transfer.

  5. Colleen…great information!

    I think one of the keys that makes a lot of sense for anyone is the transitional point of putting the fish and pond water in a container and moving that inside to adjust up in temp if need be. Then transfer over to the main holding tank the next day.

    It may not work for everyone but it’s a great way to do it if you can.

  6. I have transfered and kept my fish indoors for the first couple of years after starting a pond.I used aqariums to keep them in that i already had (many years of tropical fish hobby).If pond and fish keeping are new to you, keep in mind indoor outdoor are very simular.I like to use glass aquarium because you are able to watch the fish easly and can be blended into your home decor. To get a tank many options are avalible,buy new is most expensive but beginner type kits are readily available,the best way is check local want ads (many people just want to get rid af tank and equipment,whith luck free). Whene you set up a tank place in spot that is not high traffic and away from doors that go outside if much direct sun light also not recamended,you also need to keep in mind that maintence,water changes,and any other work lead to sum possible dripping and or spillage on floor.Whene filling tank i would use 50-60% pond water.try to treat tap water(cold only do not use hot at all) for qlorine, ammonia before mixing with pond water.when you first start the filter depending on type try to use some of your outdoor filter media,this gets bio life going quickly.I like the external canister type filter with a bio wheel the combo works well. The canister type filter can easily disconected and taken to sink or tub for cleaning and maintence whithout spills or mess.I’ve always used the rule of thumb 1 inch of fish per gallon of water to select fish tank size.10 gallons of water 10 1 inch fish or 5 2 inch and so on. This will help not to over populate.when you transfer fish from the pond use a container large enough and fill 70% pond water 5 gallon pail works for fish under 12″. when inside do not just pour fish in tank you must aclimate to temp and new water.Do this by adding tank water to container ate rate 10% of volume in 10 min intervals for 1 hour/ 10 degree difference.if container is full trade equal amounts of water from tank to contianer.this will minimize shock to thier system and stress.Advice from you local pet store always helps,but i find locally owned and operated stores are much knowlegable then franchise or chain stores. good luck.

  7. Hello Mark and fellow ponders

    I live in west central Alberta, Canada and this is my second winter with a combination totaling 19 Koi and Fantail Goldfish. I winter the fish in an attached garage in a 500 gallon stock water tank, (large round poly tank about 8 feet diameter and 20 inches deep) which has a pump and external canister type filter system.

    When I transfer the fish I fill a couple of five gallon plasitc pails with pond water and go about netting the fish. Once placed in the pails I take the pails to the garage and float the pails in a tank, let the water and fish acclimatize, slowly introducing tank water into the pails.

    The first winter I kept the water temperature in the tank around 62 F through infloor heating in the garage as well with an overhead furnace. I fed the fish over the winter to try and grow them. The first year the fish were quite small, 3-6 inches, this year they are 6-10 inches. Last year the water got cloudy and I had to change it out and clean the filter system quite often, once or twice a week. This year I was told to keep the water temperature below 55 F as to put the fish into a hibernation state. I was told this would be better for the fish and easier to maintain a proper living environment for them. Right now I am able to maintain a temperature of 50 F, I am sure the temperature will go lower as we progress more into winter. I am still experiencing high levels of ammonia and a ph level of 7.2 to 7.4, what methods can be used to lower the ammonia levels? What characteristics can be expected from the fish? Do I feed them at all over the winter or wait till spring? I have placed some rocks in the tank that are of the same type used in the pond, would these affect the ph level? Should I be adding barley straw extract and bacteria to the tank, if so where to place the medium for the bacteria? Any hints or direction would be greatly appreciated. Thanks…

  8. Hi Regan,
    Generally the advice to keep the water cool is sound since less feeding will create less waste (and ammonia build up).

    Your pH is very good, so I would try adding some bacteria to the water to help with the ammonia. If you can do water changes if ammonia get’s really high will also help reduce this.

    But let me answer the bacteria question in more detail. Please do not take this as a sales pitch, but you need to look for an all season blend of bacteria. Most stop working at 50 or lower so you need a cold weather formula.

    Also you don’t necessarily need media in the pond. We have something called the 2500 system which time releases all season bacteria from a small dispenser and works well for a lot of folks. With use, it should lower nutrient loads, and there by help with the ammonia build up to some extent. You can find this item under the small pond link towards the top of this page on the left hand side.

    This, or any applicable form of bacteria would be helpful.

    Another thing you can look for are products that reduce or eliminate ammonia directly…something called Ammo-Lock comes to mind and would be something to search online.

    Barley is good for algae control but it won’t help much with nutrient loads which is the main thing you want to watch so I’d pass on the barley products for now.

    I do think as well that as the weather cools even more, you can probably cut back on feeding pretty much without worrying. As long as it’s down near 40 degrees, and not fluctuating from say 40 to 60 or higher in the day, then you’re well past the swing stage that could go either way (if that makes sense).

    Hope this helps a bit.

  9. Hello Mark,

    I had two fish die this week…. the water temp is 48-50 degrees F, ph is still 7.2 and the ammonia is nil…. I fed them two tablespoons of Lagunia fish food on Sunday November 8th. Did I screw up by feeding them or might there be something else going on? I read that it is good to feed them a bit over the winter so as not to shock them when you start to feed them in the spring…. Is it too late to rewarm the garage to 60ish degrees F and resume feeding them…. or should I just stop feeding them altogether? I’m at a loss right now….

  10. Hi Regan,
    It’s a tough call on this one. I would say that temperature is close to the threshold where you really would want to stop feeding. Generally I think one runs into more problems the colder it get’s because then the fish’s digestive system most surely shuts down.

    As tough as it may be, once you get steadily below 50 I would stop feeding altogether. The fish can handle that. In some ways they may eat more out of habit when foods is provided and not necessarily that they need it or could even digest it.

    Really the two things I look at would be ammonia and maybe oxygen. There are other fish diseases and such but those two above are the common issues and beyond that if they check out then it could have been the feeding that caused the issue.

    You could probably bring them indoors with a gradually warming temp but I wouldn’t go that far just to feed them necessarily…they usually can do pretty well on their own without feeding once things cool down.

  11. Found your site today–another winter approaching. I live in Central AB and have had my pond for 8 yrs. Even though the pond is 42″ deep in the deep end and 2800 gals I’ve not had any luck overwintering fish in the pond. I bring them into their 300 gal indoor pond in my basement made from a wood frame and liner and running a Fluval XP filter/pump. I usually wait till the water temps get to 50F–mid October and pump water from the pond directly into the indoor pond and move the fish at the same time. The water is cold by then and the fish are easier to catch. I use some of the media from the outdoor pond in the Fluval and add zeocarb filtration to help with any ammonia changes–mostly caused by transfer and as the water temps warm up. As the pond is in the basement the indoor water temperature is usually about 70F. It takes several days for the water to warm up to that and I monitor daily for ammonia. I also feed the fish sparingly–wheat germ based until the water temps warm up then switch to Progold. Fish are fed all winter and water changes weekly. Spring is a little trickier as I have to wait until the outdoor pond temperature is within 5 degrees of their winter home. I use 20 gal tubs for the transfer and over an hour add pond water to equalize the temps. Have never lost a fish doing this although I notice the fish frequently spawn within 2 or 3 days of going back outside. I have wakins, shubunkins and sarassa comets. Even though most of them are 8 years old the biggest is only 8″ long. I think the transfers in and out may have done something to the growth hormones but at least they aren’t huge koi to net out of the pond.

  12. Regan,

    If your normal outdoor pond is set up as a natural ecosystem, your fish will need little or no added food. So if you bring a portion of that indoors with the fish (a potted plant or two, a few rocks, and a bio filter of some type), you’ll be fine.

    If not, than feed should stop as water temps reach 50 / 55 or so as Mark mentioned.

    Our pond doesn’t freeze over, so our guys stay out all year, and for feed they’re on their own all year long, no feeding is done. But you’ll be amazed (if you don’t sterilize your pond) how many things live there that the fish will eat.

    Everything from small snails, to plants, to small shrimp… the fish will actually suck in the gravel from the bottom, clean it, and spit it back out. If I stir up the bottom, or pull out some algae, the loosened critters are immediately gobbled up by the fish.


  13. My most important recommendation is to Salt Bath each Koi (separately) before putting them into the stock tank! I learned this lesson the hard way, brought all 5 Koi from Outdoor Pond to Indoor Greenhouse (approx. 600G) Stock Tank (custom built) and they were flashing and even a few Koi had visible parasites. Then I had to take each Koi out and Salt Bath each one separately, empty/refill all 600 gallons, and then reintroduce the Koi to the Indoor Stock Tank. Always salt bath Koi before relocating or when adding new Koi. Salt Bath the Koi again before relocating them back into the outdoor pond in the spring.

    In regards to bringing Koi indoors for winter, after lots of research, I built a custom Stock Tank that is 8′ x 4′ x 3′ with PT plywood and 2×4’s, 1/2″ SuperTuf Board on inside covered by the PVC pond liner, 6″ pink insulation on outside, strong ties keeping all corners of each joist fastened together, and plywood on the outside. The insulation is key to retaining the heated water, but also the insulation inside the Stock Tank makes a great ‘cushion’ for when the Koi get excited running into the sides, and also ensures that the pond liner will not tear/rip when installed over the insulation. It is very important to calculate the size of the indoor pond accurately, meaning the amount of water needs to be enough to healthily keep the number of Koi, without overcrowding with too many Koi, because that would cause a bunch of issues such as lack of oxygen.

    Remember to acclimate the Koi to the desired indoor water temperature slowly, only raise the temperature a few degrees F every 5 hours (want to avoid large swings in water temperature).

    In my experience, I only feed my Koi sping/fall diet (or similar with wheat germ type food) when water temperature is above 50 degrees F, otherwise my Koi won’t eat anyways and the wasted food settles in the tank negatively affecting the ammonia levels and more cleaning would need to be performed. Do not feed below 50 degrees F or the food will not be digested and will rot inside the Koi’s digestive system. When temperatures are above 60 degrees F, feed the Koi a high quality food and only as much as they will eat in 5 minutes.

    My setup:
    – Oase Filtral UVC 1200, that has a water feature breaking the surface to allow gases to release, UV light to clean, and carbon filter
    – Large Fluval Aerator with twenty something inch aeration stone
    – JBJ True Temp 1000 watt Titanium Heating System w/ digital controller and remote temperature probe

    Lastly, Test the pH and Ammonia levels frequently and always remember “We don’t keep Koi, we keep Water.”

    Best of Luck!
    – KodiKoi

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