Fish Pond Heaters - Controlling the Water Temperature

When it comes to fish pond heaters and choosing the right heating equipment for a pond, sometimes people can get confused about what is really necessary for their particular fish and pond. Do fish need a certain temperature of water to live? Do koi and goldfish have different requirements? What is the difference between a heater and a deicer? We’ll talk about all these topics and more on the following page. Or you can check out our video above.

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.

Pond Deicers

Deicers are the first and most common water heating solution for a pond. Generally speaking a deicer floats on the surface of the water and keeps an area ice free for gas exchange. If you have fish in your pond, keeping an area ice free allows your pond water to ‘breathe’, making sure you don’t get any harmful gas building up under the ice in your pond. Most non-tropical pond fish are fine living under the ice in a pond as long as there’s a decent deicer installed to keep that hole in the nice.

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.

Heat Exchanger  Gas Fied Boiler
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.

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

What Temperature is Best for a Koi Pond?

Many people keep koi in their ponds and do not heat the water at all. This is because fish are cold blooded and can handle cold temperatures. Even if the pond ices over, as long as you have a deicer installed to keep a hole in the ice, most fish can survive just fine. On the other hand, some people with expensive fish do choose to heat their pond or bring the fish into a garage for the winter. Just keep in mind that most heaters are very expensive to operate if the pond is not insulated. This is because any heat that is put into the pond, is quickly pulled out by the cold ground. For example, a rule of thumb for electric inline heaters is it takes 1000 watts of heat to move 1000 gallons up 10 degrees F. If you have an insulated pond and/or an insulated cover, you won’t need as large of a heater.

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, most 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.  But again, there are many others that do not heater their ponds at all with many reports of very healthy koi.

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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