Pond Temperature Guide (Plus, Our Best Pond Thermometer Pick)

by Tory Jon | Last Updated: August 23, 2021

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How Does Water Temperature Effect Your Pond?

As outside temperatures change throughout the year, inevitably so does the water temperature of your pond.

A common misconception is that pond temperature only matters when the temps get too cold. However, warm pond water has its own set of issues.

Then throw in rapid temperature swings and things can get really interesting.

Let’s look at how pond temperature can affect first your ponds fish, then it’s eco-system in its entirety.

Effects On Pond Fish

Water temperature can affect your pond fish in a number of ways.

Warmer pond water, by nature, has less oxygen than colder water. And if the temperature of your pond water gets too warm, then there might not be enough dissolved oxygen in the water for your fish to thrive and can even result in fish kills.

When the water temperature of your pond reaches roughly 85F (30C), then your fish are in danger of not having enough oxygen. You’ll notice your fish become sluggish and stop feeding as their metabolisms slow down to adjust for the lack of oxygen.

To combat this, it’s important to properly aerate your pond to ensure your fish have the oxygen they need to survive. Check out our review of the best pond aerators on the market.

You can also run a water feature like a pond spitter, fountain or waterfall to help add vital oxygen to your pond.

And remember to adjust your feeding schedule when the water gets warm and your fish start to slow down. They are entering a resting state called torpor in which their metabolism sharply declines, and they won’t require as much if any food (see Do Pond Fish Hibernate in Winter? for more information). This typically happens to pond fish in winter but can also happen when pond temps get too high. This is a common time to overfeed your fish, which just contributes to poor water quality conditions and even less oxygen in the water.

Conversely, when pond temperatures start to drop your fish can be affected, as well.

Most hardy pond fish, like koi and goldfish, will be fine as the water temperature drops. In fact, as long as the water in your pond doesn’t completely freeze solid, and you maintain a hole in the icy surface, your koi and goldfish should survive.

Again, they will start to enter a form of hibernation called torpor, when the water temperature reaches around 50F. When this happens, it’s important to again adjust your feeding schedule.

Temperature	Feedings
Above 60F (16C)	Up to 5 times a day
50 – 60F (10 - 16C)	Once a day
40 – 50F (4 – 10C)	Once every other day
Below 40F (4C)	Do not feed

And be sure to feed your fish a high-quality food, as well! Low-quality food will only add to the ponds sludge problem as fish tend to excrete out the fillers that go undigested. I recommend Kaytee Koi’s Choice Premium Fish Food.

Effects On The Ponds Eco-System

As we previously learned, warmer pond water equals less oxygen in the pond. Of course, your fish don’t like the decrease in dissolved oxygen, but neither does your pond’s eco-system, including beneficial bacteria, pond plants, and other organisms you have in your pond.

And you can see the domino effect that takes place, as lower oxygen levels start to kill off vital beneficial bacteria levels and oxygenating pond plants, creating even more water quality issues.

This again is where proper pond aeration comes into play. Adding dissolved oxygen to your pond is an excellent way to ensure that not only your fish but the whole eco-system benefits.

Also, keep in mind that as water temperature increases, the PH level of your pond decreases. And vice versa. So, as your temperature swings, it’s always a good idea to use a pond water test kit to ensure that your pH levels, ammonia, and nitrite levels are in check.

Pond Water Temperature Vs Air Temperature

It’s important to understand that water temperature takes a considerably longer amount of time to heat or cool compared to the air temperature.

When we talk about pond temperature, I am referring to the actual temperature of the water. If it’s 85F (30C) outside, your pond’s water temperature can still be considerably colder.

Plus, depending on how deep your pond is, the top of the pond, or the water near the surface, will most likely be a different temperature than the bottom of your pond. We’ll get into this more later as we learn how to properly measure pond water temperature.

All of the organisms in your pond are influenced by water temperature, not the air temperature. So, let’s now look at the ideal water temperature ranges for your pond.

Ideal Pond Temperature Ranges

Just as we humans have an ideal temperature range, though that range varies widely between my wife and me, fish and other pond life have an ideal range, as well.

The ideal pond temperature range is between 68° and 74° Fahrenheit (20 to 23C).

And that range holds true whether you have a koi pond (or any type of fish pond) or a pond without fish.

Of course, your pond temperature in summer may be drastically different than your pond temperature in winter. And those temps may fall out of the ideal range, which is typically fine.

When the pond water temperature in winter starts to drop below the ideal range, as long as you have hardy fish like koi and goldfish, ensure enough dissolved oxygen for the fish to survive, and your pond doesn’t completely freeze solid, your fish should survive. Check out our full guide on how to keep pond fish alive in winter for some important tips.

Conversely, when water temperatures start to rise in Spring and during the warmer months, they’ll potentially rise passed the higher end of the ideal temperature range. The biggest concern is going to be oxygen deprivation, which is why I highly recommend a pond aerator to add dissolved oxygen to your pond.

How To Measure Pond Water Temperature

To measure the water temperature of your pond, you simply use a pond thermometer.

And remember, the water temperature on the surface of your pond will differ from the temperature on the bottom of your pond. You can easily get readings from both by using a floating thermometer and a submersible thermometer.

Let’s take a look at a few of the best pond thermometers available today.

Pond Thermometer Reviews

There are three main types of thermometers you can use to measure your pond’s temperature. Each has its own pros and cons which we’ll discuss below.

Floating Pond Thermometer

A floating pond thermometer does just that, it floats on the surface of your pond and allows you to get an accurate reading of your pond’s temperature at any time.

Simply place the thermometer in your pond and you’re ready to go. Most of them, like the DaveSpa Floating Pond Thermometer below, has a string attached to it, as well, so you can anchor the thermometer to land and easily pull it out of the pond.

The one down-side to floating pond thermometers is that they only measure the surface water of your pond. If your pond is more than a foot or two deep you may need a separate submersible thermometer, as the water at the bottom of the pond will be a different temp.

Digital Submersible Pond Thermometer

A submersible pond thermometer is essentially a digital thermometer that has a long cable with a probe attached to the end of it. You basically lower the probe into your pond to get a temperature reading of the water near the bottom.

An important thing to note is the length of the cable attached to the thermometer. For most backyard ponds the cable length probably won’t be an issue. But, if you have a fairly deep pond or lake, for example, 20 feet deep, then a cable length of 1 foot won’t give you accurate readings. Look for a thermometer with at least 3 feet of cable to get a good, deep temperature reading.

The Qooltek Digital Submersible Thermometer has 3.3 feet of cable and can be surface mounted near your pond for year-round readings any time of the day. Its battery operated and can display temps ranging from -58 to 199F.

Infrared Pond Thermometer

Infrared thermometers look like a phaser from the Star Trek movies, but they are actually an extremely easy way to get a temperature reading of the surface of your pond.

You simply point the thermometer at your pond, pull the trigger, and an infrared beam measures the surface temp quickly and accurately.

They also come in handy to get a temperature reading of just about anything – your pond’s pump, hot engine parts, your dog – which makes them a very handy tool to have around.

Unfortunately, infrared thermometers can only measure your pond or water gardens surface temperature.

The Etekcity Digital Laser Infrared Thermometer is one of the best thermometers for the money. It gives you extremely fast temperature readings of any object from -58 to 716F!

Pond Temperature Control

So, what do you do when your pond starts to raise or lower out of the ideal temperature range? In other words, how do you control the temperature of a pond?

First, understand that almost every pond goes in and out of the ideal temperature range. You’re not alone. And as long as you stock your pond with hardy fish (like koi and goldfish), they’ll most likely be fine as long as they get the dissolved oxygen they need to survive and thrive.

When pond temperatures start to fall, you can control the water temp with a submersible water heater.

I would typically only recommend this if you expect your pond to get extremely cold. I’m talking “potentially freezing solid” cold. Otherwise, a pond de-icer will usually suffice. A de-icer simply keeps a hole in the icy surface of your pond to allow for oxygen to enter the pond and dangerous gases to escape.

Conversely, when your pond’s temperature hits roughly 85F (30C), you can cool your pond and add oxygen by:

• Pond Aeration – Not only does a pond aeration system add vital oxygen to your pond, but the circulating water is also cooler and can help control the pond temperature.

• Oxygenating Pond Plants – Pond plants are a great addition to any pond. They add oxygen to the pond’s water, and they also help shade the water from direct sunlight, helping to cool it down. Plus, fish like to hide out in the shade provided by these plants! Be sure to utilize floating pond plants for the best shade protection.

• Add Cool Water – I'm not talking about dumping ice water in your pond here. But, in the summer heat, your pond will naturally lose water due to evaporation. So, you’ll want to replace any lost water. This will help cool the water and ensure your pond’s water level doesn’t fall too low. Just be sure to treat your tap water with a dechlorinator before adding it to your pond.