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Winter Aeration

Winter Aeration

As the cool weather comes, your fish go into hibernation and you shut your filter down for the season. Though things slow down, not all the natural processes in your pond come to a complete halt. The organic debris that accumulated during the summer and fall will continue to decompose, and as it does, gasses will be released into the water column. Moreover, those excess nutrients act as a fertilizer and will fuel winter algae growth.

During these frigid months of the year, keeping the pond oxygenated and keeping a hole open in the ice, means the difference between life and death if you keep your fish in the pond for winter. When a layer of ice forms over the surface of your water garden, it essentially eliminates any transfer of air to or from your pond's water. What this means to you is that, as debris decompose and your fish consume oxygen, byproducts are produced in the form of gasses that are toxic to your pond's inhabitants. These gases are trapped under the ice and cannot escape; fresh air from outside the pond cannot reach the water either and so begins the process of the winter fish kill.

So, you may ask, what is a pond owner to do so the bad gases are released and your fish stay happy throughout the winter? Here are some winter pond care tips that will help you prepare. Bubblers and de-icers both keep a hole open in the ice, but they go about it differently.


A de-icer, like the K&H Thermo-Pond 3.0 De-Icer, is not a heater, but is designed to maintain an open hole in the ice to allow for gas exchange. Heaters are more frequently used in aquariums, particularly those that house warm-water fish like Tetras, Danios or Angelfish. In your pond, the fish will overwinter just fine without a heater--even if temperatures drop below freezing.

When selecting a de-icer, make sure to check what the maximum pond size the unit is rated for. Each manufacturer recommendation does vary, but in general, de-icers with greater wattages can be used in larger ponds. Most de-icers are thermostatically controlled to turn on when the water temperatures are around 35 degrees to help cut down on energy costs however cold water takes a long time to warm up, leaving your de-icer running more often than it needs to. Plugging your de-icer into the Thermo Cube Thermostatically Controlled Outlet will help as it is regulated by air temperatures, not water temperature. Thus, when the sun is shining, and air temperatures warm up, the Thermo Cube automatically cuts power to the de-icer and turns it back on when the air temperature drops. The combination works flawlessly - applying heat when it's required to keep the ice open and shutting it off when it's not.

While a de-icer is effective, during cold windy nights they may not be enough to keep a hole open on their own. If your vent does freeze over during extra cold temperatures, for long periods of time, simply pour hot water on the ice where the hole once was. It will melt the hole back open - and your fish can breathe a sigh of relief! Be sure not to use sidewalk salt or similar products. Sidewalk salt is made for one simple purpose: to melt ice on your sidewalk. And while it theoretically could be used to melt pond ice, it's most definitely not the right product for the job since many contain additives like chloride which is not fish or plant friendly.

Aeration Kit

Winter is one many times where aeration kits are a valuable asset for anyone with a water garden. Aeration kits infuse oxygen by releasing tiny air bubbles from air stones or diffuser sticks, which move the water allowing for gas exchange. During the winter, we recommend moving the diffuser sticks to half your maximum depth. This will help to reduce ice formation and keep a pocket of warm water for your fish at the bottom of the pond. Have questions on how to know which kit is right for your pond? Check out our article How to Choose an Aeration Kit.

If you have an aeration kit, pieces and parts do need to be maintained so if you've been using your aeration system for the summer or it has been dormant since last winter, it will need some attention. Check to make sure the air stones/diffusers are working properly and install a maintenance kit to ensure it's working to its full potential.

Combine a De-Icer and Aeration Kit

Water gardens in colder climates may need a little extra. For these pond owners, the CrystalClear PondAir & Thermo-Pond 3.0 De-Icer Combos are the perfect option. Using a de-icer and aeration kit together will ensure that a hole is kept open, water circulates properly, and your dissolved oxygen levels remain high. Additionally, using a pond aeration kit during winter will allow you to use a smaller wattage de-icer, which could add up to some serious savings on your energy bill.


Many owners look to use equipment that they already have and rely on their pump to keep the pond open during winter. Pumps do an excellent job at circulating water, but they may not be the best option. Most pumps are not designed for winter use as the freezing water moving through them could cause damage. In contrast, aeration kits are designed to be used year-round and freezing temperatures will not do them damage. Another reason to consider using a pond aeration system for the winter is the operating cost. Pumps can get expensive, but aeration kits can cost as low as $0.20 per month to run 24/7. If you do decide to use your pump during the winter, double-check your product manual for specific recommendations from the manufacturer.