Why is it important to keep an opening in the ice on a pond during the winter?
Making sure you have an area free of ice is crucial for koi ponds or ponds with fish to allow proper gas exchange. A koi pond is essentially dormant during the winter months and the biological activity is at a minimum. However, this does not mean there is no biological activity. The respiration of the fish and the metabolic processes is still occur, steadily releasing waste products while using up oxygen. Without an opening in the ice, harmful gasses such as carbon dioxide remain trapped under the ice and the supply of dissolved oxygen steadily decreases. If this continues to progress and oxygen is not replenished, the fish will not survive the toxic environment and they will fall victim to what is commonly referred to as “Winter Kill.”
What is the best way to provide an opening on the pond surface?
There are several ways of maintaining an opening in the ice on a pond. But, never use physical force to break an opening in the ice. Fish are very sensitive to vibrations and hitting the ice can stun or severely injure fish. Thermostatically controlled de-icers are one method used buy many. They are easy to use, energy-efficient, and maintain an opening in the ice, even in below zero temperatures. Please note that a de-icer is not a water heater and they are not designed to raise the water temperature of the entire pond. They are designed to maintain an opening in the ice to allow gas exchange. Also be aware that a de-icer in not full proof and may fail, should this occur you will need to replace it ASAP to maintain the opening.
Many koi pond owners have learned that by building a pond covering, it will help to hold in the thermal heat from the ground and the cover will act as a greenhouse trapping in the heat. If done properly the cover will support the snow load and trap sufficient heat to prevent the pond from developing a thick layer of ice making it easier for the water surface to remain open regularly.
How large an area do I need to keep open?
A small hole of say 10″ will support oxygen and gas exchange. You do not need, nor should you expect, to keep a large areas of your pond open in frigid northern zones.
I’ve placed a de-icer in my pond, but it isn’t keeping the ice open. What can I do?
When using a de-icer, keep in mind that heat loss is very rapid in the the winter, so the heat the de-icer is producing will dissipate quickly. Try place the de-icer near the shallowest part of your pond. This will help minimize the heat loss to the air, you can also try block the wind directly around and over the unit. Some koi pond owners make a sheet of plywood directly over a small corner of their pond where they’ve placed a de-icer to maximize the efficiency of the heat being produced.
Will my de-icer raise the temperature of the water?
De-icers are designed only to allow a small opening in the ice. A pond de-icers will not heat the entire pond.
Can I use an aerator to keep my ice open?
Yes, an aerator is an effective way to keep water open in the winter. It agitates the surface to keep a small opening in the ice. It’s important to house the air pump in an insulated box, so that it uses somewhat warmer air than the outside air. If the pump is pulling cold outside air it can be difficult to maintain airflow when moisture condensation inside the airline tubing – it could cause the airline to freeze, which would plug the bubbler. It’s also important not to placing the bubbler on the bottom of the pond, as it will stir up any sediment or rapidly cool the overall pond water temperature by mixing colder and warmer water layers. Place the bubbler near the pond water surface at the edge or shallowest part of your pond.
How can I keep my pond open if I lose power in a winter storm?
In the event of a power loss a generator can be used to provide power for the pond. You may want to think about purchasing a battery back-up system to operate your pond equipment. This is a situation were having a pond cover comes in very handy, as the pond cover will help to hold in the heat and slow down or even prevent the pond from freezing over.
Should I stop feeding my fish as soon as the temperature changes?
Measuring water temperature is the most accurate way to determine when to change over to a winter staple food and more importantly know when to stop feeding. As the water temperature drops you need to be aware of the metabolism of the fish. As the water drops below 50°F you should stop feeding. Just like in the spring as the days start to warm up many pond owners are anxious to start feeding their koi again. On the first warm day of spring, the air temperature may read above 50°F but the water temperature will still be much lower. Be sure to check the water temperatures throughout the day to get an accurate reading. If the average water temperature is above 50°F for several consecutive days, then you can start feeding a spring staple diet.
Will the freezing temperature kill all the beneficial bacteria in my pond?
No, the colder winter water temperatures will reduce the population of beneficial bacteria and slow their biological activity, the majority will survive the winter. Nitrifying bacteria continue to process organic material throughout the winter and seasonal cold water bacteria will remain active.