A Greener View

God made water as a unique substance. At about 40 degrees F., it is denser than water warmer or colder, so it settles to the bottom of the pond. It forms a puddle that if left undisturbed will not mix with the colder water above it. The ice floating on the top of the pond insulates the lower water from even colder air above it.

Winter pond temperatures can remain very cold for many months in northern climates. There's only so much water in a pond. There can only be so much oxygen in the water. If the ice caps over the pond, the fish, other animals and any decaying organic material may eventually consume all the oxygen and the fish will suffocate.

This is referred to as "winter kill" and occurs commonly in natural ponds and our over-stocked backyard ponds are much more susceptible. It's easy to avoid this by simply keeping a small area of the pond ice-free for the exchange of gases with the atmosphere. Air bubblers and small pumps can be used to keep small areas ice free, but do not allow them to mix the lower 40 degree puddle of water with the colder top layers. They cost less to run than deicers, but do not work when the air temperature drops below the teens for extended periods of time. Any small air or water pump that creates a flow of water across the pond that disturbs the bottom puddle of warm water will eventually lead to a fish kill.

Pond deicers are not meant to warm the pond, but just to keep a small area free from ice cover for the exchange of gases with the atmosphere. Most are set to turn on around 34 degrees and off at around 40 degrees. Keep the heating coil on the deicer clean. Mineral deposits can build up on it, insulate it from the water, and cause the unit to fail. The heating coil can be dipped into lime-a-way or vinegar to dissolve the deposits.

In one respect, all heating devices work the same, because physics is involved. It takes a specific number of calories of heat energy to raise the temperature of an object a specific number of degrees. It does not matter how the heat is applied or how long it is applied. A single candle at a time over a period of time will generate the same number of calories as a blow torch over less time. If the object being heated is sitting in the freezer and therefore giving up heat at the same time it is gaining heat, it will take longer to warm up and if it is cold enough, it may not warm up at all. So, smaller wattage deicers run longer in northern ponds to do the same work as a bigger wattage deicer does on shorter time. But, the same amount of electricity is used and the electric bill will be identical too. In the coldest weather, a larger wattage deicer will work to keep the ice open that a smaller deicer can not do. If a pond is in a protected location, a smaller deicer may still work.

To make any deicer more efficient, use something to insulate it. If the deicer can be set in the corner of the pond so it can be covered with a plastic dome or plywood shelter, so it is some sort of a roof over it that traps lost heat, it will work to colder temperatures. Snowfall will not bother the deicer, since it is just above freezing, the snow will melt around it.

If the fish are gasping for air at the surface, this may indicate either low oxygen or excess toxic gases, like hydrogen sulfide or carbon dioxide. Find a way to enlarge the hole for better gas exchange using another bubbler or heater. Do not pound on the ice. If necessary, use a garden hose to melt a larger hole. Use dechlorinator if necessary.

Water features that run during freezing weather can create beautiful ice sculptures. Running the waterfalls and stream in winter when temperatures drop below freezing may create ice jams and leaks in the watercourse. These leaks cause the overall pond level to lower, giving the fish less water. The ice itself is a temporary leak, as that water does not make it back to the pond. As the water level in the pond drops due to these temporary leaks, it could get below the skimmer door opening level. This could cause the pump to burn out and the pipes to freeze with what water they have left in them. Also, warm pond water mixing with the very cold air could result in excessively cold water temperatures that will harm the fish.

Bottom drains that are left circulating or waterfalls and streams that fall into the pond and mix the ‘warm' water off the pond bottom with the cold air will chill the fish to a lower unsafe temperature. These pond designs will also allow the pond water to freeze to a thicker and deeper level. If the 40 degree puddle is left in the pond, the ice can not freeze as thick until the puddles gives off its heat. If the water has been mixed, so there is no puddle, the heat is gone and the ice can replace the water very quickly. Especially if the water stops moving from low water levels that stop going in the skimmer or if the power shuts off. Remember, only liquid water can give its oxygen to the fish.

When shutting off the system for the winter, close the bottom drain, remove the pump, filter mats and any other items from the pond, skimmer and biological filter. They can be cleaned, dried, and stored in a garage or basement until spring. Disconnect the auto-fill valve from the water source to reduce the possibility of freeze damage. Flexible PVC pipe does not have to be drained, but if desired, a shop vac or leaf blower can cleanout the line.

The pump may need additional care beyond cleaning. Refer to the pump's owner's manual for additional information. Some pump brands recommend that the pump be stored them in a location where it will not freeze, submerged in a bucket of water to keep the seals hydrated. External pumps can be drained and depending on the climate, removed for the winter based upon manufacturer's recommendations. External devices such as ultraviolet lights also have winter care needs, consult their manuals also.

The skimmer should be left full of water and it will survive freezing just fine. Water is freezing in the box at the same time the water in the ground is freezing, so they push against each other. A biological filter box that has water at the bottom that will freeze and expand against the soil that is not yet frozen, should be drained and then covered, so no snow melts into it and freezes. Empty filter boxes might benefit from having a stick or board left in them to allow a small animal an escape route should it fall into the box.