During the winter months, a hole must be maintained in the ice. As ice forms on the pond, toxic levels of gases from decaying organic matter can be trapped under the ice. This creates a toxic gas chamber for the fish.
A pond heater floats on the surface of the pond and creates an ice opening allowing the gases to passively escape. They typically have an internal thermometer and will turn on and off depending on the temperature of the water.
An aerator is an air pump that sits outside the pond. It must be protected from rain and snow. Typically placing them on a elevated surface and covering them with a cover rock works well to protect them from the elements. The aerator have air stones which are placed in the pond. They should not be placed in the deep section. Ideally they are in 6-12″ of water.
You can install these items when you install the netting so that you are all set in case cold weather arrrives unexpectedly with ice forming on the pond.