In the northern climates this is a question that I hear quite often. Do I need to install fish pond water heater or pond aeration equipment? Let me begin by saying if you don’t have fish in your water garden it is not necessary to install either one. An argument can be made that one is more important than the other, however both can keep an area of the pond surface free from ice.
During the winter months your fish are still producing waste and CO2. Decomposition of the fish waste and any organic material during the winter produces harmful compounds that will rob the water of oxygen causing stress to the fish. If water toxicity levels get too high the fish could die. When the pond is not frozen the gasses escape through the surface. Thus it is essential to keep an area in your pond free from ice. Both a fish pond deicer and a pond aerator pump have positive and negative points, so let's take a closer look at both.
FISH POND DEICER: This is the easiest way to keep your pond free of ice. The electric pond heater is designed to heat the area around it, not the whole pond. It will not change the overall temperature of the pond water. Most electric pond heaters are thermostatically controlled therefore it can be plugged in and it will work. The negative side to heaters for a pond is if it gets really cold or windy the space around the fish pond water heater can freeze over creating a dome. It's important to protect the fish pond heater from the wind, and if it gets really cold, check it often to see if it is frozen.
AERATORS for PONDS: The pond air stones do a good job of keeping a space open in the ice. Exactly what is pond aeration? A pond aeration system adds oxygen to the water column. As the air is moving through the water it allows the organic compounds that are in the water to attach and when the bubble hits the surface the gasses break apart releasing them safely into the atmosphere. The negative to pond aerator pumps is the potential for the cool air to super cool the water. During winter months, keep the air stone a foot above the bottom of the pond keeping the warmer water just below the air. If the air compressor is out in the cold air it is transferring that cold air to the pond water. This could cause the fish to die. Consider covering the winter pond aeration system with an insulated cover or put it in a heated building.
Some pond owners use a combination of both a winter pond heater and pond aerator. Just be sure to do one or the other. Lastly, remember a pond aerator can be used for other maintenance projects.