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How do I prepare my fish for winter? Do I need to bring them inside? – Water Garden & Features Q & A

Allow harmful gases to escape by adding a diffuser.

Water Garden & Features Q & A

Q: How do I prepare my fish for winter? Do I need to bring them inside? – Liz in Michigan

A: As the temperatures fall, we may be pulling out our winter coats and goulashes, but your fish don’t need them at all! In fact, pond fish, like koi and goldfish, do quite well in a pond over the winter – even if it freezes over – as long as your pond is at least 18 inches deep (though we recommend 24 inches to be certain the fish don’t turn into popsicles). The fish will go into their annual torpor, or dormancy, and will require little more than clean, oxygen-rich water to survive.

To ensure they get that life-sustaining oxygen, you will need to do four things:

1. Remove debris from the pond. In the fall, before ice forms, give your pond or water feature a good cleaning. Remove debris, trim dead leaves off plants, net floating leaves and remove as much detritus as possible so very little will be decomposing – and releasing harmful gasses – through the cold months.

2. Add some beneficial bacteria. Also in the fall, you may want to add some beneficial bacteria, like Pond Logic®’s Seasonal Defense®. It accelerates the decomposition of leaves, scum and sediment that builds up during the fall and winter months. In the spring, it replenishes winter bacteria loss, jump starts the filter and breaks down unwanted waste, making your pond water ready for a clean spring and summer.

3. Install an aerator or air stone. Colder water holds more oxygen than warmer water, but you’ll still want to inject air into the pond during the winter months, especially if your pond freezes over. One or two air stones or a diffuser placed in a shallow part of your pond will be enough to aerate the water and keep a small hole in the ice, which will allow harmful gasses to escape and oxygen to enter.

4. Hook up a heater. If you live in a frigid area where the ice on your pond builds to an inch or more, you can use a floating heater or de-icer, like the Thermo-Pond, that melts through the ice. Again, it’s critical to keep an open hole in the ice to allow for gas exchange.

In most cases, your fish will be just fine through the winter months. When the water warms, you can begin feeding them again and enjoying them for yet another year!

POND TALK: How do you prepare your fish for winter?

10 Responses

  1. Wow.. thanks for posting!

  2. I have a small container pond (100 gal) with a waterfall and in winter I had an old tent so I cut the bottom out of the tent and I cover the pond with it. It helps to keep debris out and if it should freeze over I hang a trouble light with a 60 watt light bulb and voila it thaws out pretty quick. We live in northern ohio so we get some pretty cold winters here.

  3. The above question was how to prepare the fish for winter. Your answer was preparing the pond. How do i prepare the fish – like cjange of diet, if so what and how?

  4. I was thinking about putting an air stone in my pond but I was wondering about pumping all that cold air into the depths of the pond. Especially when it gets down to zero (or lower), won’t that tend to freeze things up even quicker?

    • Jerry,

      Sorry this reply took so long to get to you! That is a good question. I can honestly say I haven’t seen any issues with placing an aerator in a small water garden for the winter in the northern climates. You make a good point, but I haven’t seen any fish freeze solid yet because of the cold air being pumped into the water. An aerator or de-icer are both great ways to keep a hole open in the ice and keep your fish safe during the winter.

  5. I wonder why my fish have quit eating. It’s only September 26th. They aren’t eating much at all.

    • Date doesn’t really matter it is the water temperature that will determine when your fish will show down their eating behavior. You should also look at the type of food you use for different temperatures.

    • We have two pre-formed garden ponds, each just barely 18″ deep. With a heater/defroster in each one, the goldfish have made it through 4 winters so far. I stop feeding them when the water temp stays at 50 degrees or lower and don’t resume feeding them until it stays at 50 degrees or higher in the late spring…a period of almost 6 months without food. I make sure the water has a good salt reading to help the fish develop a good slime coat to fend off disease during this time. Since we have a good-sized frog (bullfrog?) that winters over with the fish, I leave a layer of leaves on the bottom and also sink a 3″ deep x 8″ square box of soil down to the bottom of the pond. I really don’t know if the frog (Sumo) burrows into the mud or the leaves but, so far, so good. He trusts me enough to let me “pet” him on occasion. I will really miss him/her if he disappears. He was gone about a month in the early summer and I thought the raccoons had gotten him and then one day he reappeared and has been here since.

      • The frog has made it through 3, maybe 4 winters. The only one of ours that has ever lived through the New England cold!

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