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Fish Pond Heaters - Controlling the Water Temperature

Although fish pond heaters are not absolutely essential to the survival of koi or other fish in many environments, using one definitely helps provide more control over your pond environment, and thus the physiology of your fish. Some koi keepers heat their pond water to a certain minimum temperature all year round, while others vary the temperature in an attempt to imitate the natural temperature variations in Japan where koi originate. In areas that experience very cold temperatures, pond heating equipment can help manage ice build up, or even prevent a pond from freezing solid in cold enough temperatures.

Types of Fish Pond Heaters

There are three main types of fish pond heaters that have become popular: Gas-fired boilers, inline electric water heaters and deicers. As a koi pond heater, all work well at their intended purpose.

Heat Exchanger  Gas Fied Boiler
A heat exchanger from a gas-fired boiler heating system

Gas-Fired Boiler with Heat Exchanger

With a gas-fired boiler, water within the heating system (not the pond water) is heated in a gas boiler and then circulated into a heat exchanger. At the same time, pond water is pumped into a separate chamber in the heat exchanger, which absorbs heat from the hot water in the neighboring chamber before being returned to the pond. A gas-fired boiler system works very well as a koi pond heater.

Inline electric koi pond heater
A heat exchanger from a gas-fired boiler heating system

Inline Electric Water Heater

With an inline electric water heater, water is pumped into the heating chamber where it encounters an electrical heating element. As the water passes through the heater before being returned to the pond, the element warms the water slightly, effectively achieving a desired temperature over time.

Pond Deicers

Pond deicers are the least expensive water heating solution for a pond. Because the heater generally floats on the surface or is submerged in the pond in a single location, the water is not circulated through the heater, which creates a somewhat unbalanced heating situation. However, if your primary goal is only to keep an area of the pond ice-free so that gas exchange can occur between the water and the air, then a deicer will achieve that goal.

What Temperature is Best for a Koi Pond?

As mentioned above, there are varying theories on what temperature a pond should be kept at for optimal koi health. While some koi keepers use fish pond heaters to keep their ponds at a constant temperature all year round, there are others that believe koi need a 'resting period' similar to what they might experience in a typical short, but harsh Japanese winter. To emulate this, a proven temperature regime is to heat the water to a minimum of 13 degrees Celcius (55 degrees F) for 40 weeks, then slowly lower the temperature by a degree each day until the temperature of the water reaches it's natural temperature. At this point the fish pond heater can be turned off for six weeks. After the six-week period is up, the heater can be turned back on while increasing the temperature by one degree each day until the pond is back to normal operating temperature. If by chance you live in a very cold climate, it is a good idea to keep your heater on a low setting for the 6 week resting phase to keep your pond operational and free of ice.

Pond Ecosystems

Changing one thing in a pond often has an effect on everything else in the pond due to the delicate ecosystem balance in place. Changing the temperature of the water is no exception, and the repercussions should be fully understood before taking action.

Temperature and Dissolved Oxygen

The temperature of water has a direct correlation to the amount of dissolved oxygen naturally present in the water. The colder the water, the more oxygen is readily available for use by koi and other fish. As the water is heated, either by nature or through the use of a fish pond heater, the solubility of oxygen decreases, effectively lowering the amount of oxygen available in the water.

How temperature affects disolved oxygen
A heat exchanger from a gas-fired boiler heating system

As an added complication, the activity level of koi fish increase as the water temperature increases, which places additional demand on the available oxygen in a pond. In the winter months, or when the pond water is cool, a koi will become quite lethargic, eating less and as a result producing less waste. As the water is heated and the activity level of a koi increases, it will require more food and more oxygen to carry out growth, tissue repair and reproduction. Therefore, it is important to monitor the dissolved oxygen levels, keeping them above a minimum of 6 mg per liter of water. If oxygen levels are allowed to decrease below this amount, a potentially dangerous situation could be created for koi or other life in the pond. The easiest way to increase oxygen levels is by using an aerator.

There are other factors in a pond that will affect the oxygen levels as well. For example, pesky blanketweed uses oxygen and produces carbon dioxide. As well, beneficial bacteria in the biological filter system will naturally use oxygen as part of the water cleaning process. Read more about biological filtration here.

It is also possible to have the opposite problem on your hands; too much oxygen. Gas bubble disease in fish is one potential side effect of supersaturated water. Readings above 12 mg of oxygen per liter are getting high, and the source of the super saturation should be identified and rectified as soon as possible. One common cause is the photosynthetic process of certain plant life in the pond, especially certain types of algae. If the water in your pond is supersaturated with oxygen, the levels can be brought down by aggressively agitating and splashing the water to allow the excess oxygen to vent off.

In closing, fish pond heaters are an excellent way to gain a little more control over the ecosystem in your pond. Have a question related to which pond heater you should buy? Send us a message and we'll be sure to respond as soon as possible. Click here to go to our contact page.

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