How to Measure Pond Water Temperature

Testing Surface Water

Use a handheld or floating thermometer. To test surface water, you only need a thermometer that can dip just below surface level. You can use a handheld thermometer made for water, or you can use a floating thermometer that’s meant to float on top of the pond.Tip: If you are using a handheld thermometer, make sure it is made specifically for water so that it’s airtight. You can find water thermometers at most outdoor supply stores. Floating thermometers usually have a length of twine attached to them so you can tie them off and leave them in the pond for long periods of time.

Set the thermometer probe 1 in (2.5 cm) below the surface. If you are using a floating thermometer, position it so that the floaty is at the top and the probe is at the bottom. For a handheld water thermometer, put the probe into the water about 1 in (2.5 cm) below surface level.

Wait for about 30 seconds for the thermometer to take a reading. If your thermometer has a digital reading attachment, it will show you the temperature on the screen. If you’re using an analog one, take a look at the numbers and figure out where the red line is to get your reading. Thermometers with digital readings are nice because you can keep it in the water as you read the temperature, which can give you a more accurate reading.

Measuring Deep Water

Attach a weight to a water thermometer or use a digital thermometer. If you only have a handheld thermometer, you can tie a weight or a rock to it with twine to make it heavy. If you have a digital thermometer with a probe, you can hold onto the digital reading screen while you lower the probe down. Most probes have a wire that’s about 1 m (3.3 ft), so it will be deep enough to reach the bottom of the pond. If you are using a handheld thermometer, make sure it’s waterproof and airtight with a length of twine attached to it so you can pull it up.

Lower the thermometer into a deep area of the pond. Usually, the middle of the pond is the deepest area. Slowly lower your thermometer into the water until you hit the bottom, and try to hold your thermometer steady. If the pond is large, you may need to take a boat out to the middle.

Wait 5 minutes to get an accurate reading. Deep water thermometers need a little more time to adjust to the colder temperatures. Keep your thermometer underwater for about 5 minutes or until the temperature reading stays steady.Did You Know? Even though ponds contain still water, they still have small “currents” that can affect your temperature reading.

Test the temperature of 2 to 3 locations to get an average. Bring your thermometer up out of the water and move to another location that’s also pretty deep. Take 2 to 3 more readings of the deep water, then add up the temperatures and divide them by the amount of readings you took. For example, if you took 3 readings at 56 °F (13 °C), 61 °F (16 °C), and 59 °F (15 °C), add them together to get 176 °F (80 °C). Then, divide that by 3 to get 58.6 °F (14.8 °C) for your deep water temperature.

Monitoring the Pond Temperature

Keep the water between 60 and 75 °F (16 and 24 °C) in the summer. Surface water is more prone to fluctuation because it’s closer to the air around the pond. In the summertime, try to keep your pond cooler than 75 °F (24 °C) at the surface for the health of the fish and the plants.Warning: Water that is too warm deprives fish and plants of oxygen, so they aren’t able to breathe as well and they could die.

Use a water heater during the winter months if your pond might freeze. If you have a small pond on your property and you’re worried that it could freeze solid, install a pond water heater to the inline pipe of your pond to warm the water as it enters. Try to find a 250 watt water heater for the best results, and make sure you only use it when it’s below freezing out so the water doesn’t get too warm. You can find water heaters at most home goods stores.

Plant pond plants to provide shade in the water during the summer. An easy way to keep the water cool in your pond is to use shade from plants in and around your pond. Try using floating water garden plants on the inside of your pond to keep your fish cool.Did You Know? Plants also help provide oxygen to the water which will keep your fish and ecosystem healthy. Water lilies, water lettuce, and sweet flag are all floating pond plants that provide a lot of shade.

Add in cool water during the summer to lower the temperature. If you notice that some of the water in your pond has evaporated, treat some cool tap water with a dechlorinator and then pour it into your pond. This will help to cool down the entire pond as well as keep the water deep enough for the plants and the fish. Ponds naturally lose some water in the summer due to evaporation, so you don’t need to worry about it if you see the water level start to drop. You can add 20% of your total pond water into the pond to cool it down. For example, if your pond has 100 gallons (380 L), you can add in 20 gallons (76 L) of water.

Install a pond aerator if the water is too warm. Pond aerators add oxygen to the water, and they keep the water circulating so it doesn’t stay still. Put one of these at the bottom of your pond and use it during the summer to keep the temperature cool for your plants and fish. You can find these online or at an aquatic store near you.

Move your fish to a tank if the water drops below 50 °F (10 °C). In the winter time, try to keep your pond warm enough so the fish can still swim around. If the temperature of your pond dips below 50 °F (10 °C), it could be in danger of freezing. Transfer your fish to an aquatic tank until the threat of frost is over. Most fish can survive if the surface of the pond freezes over, but they can’t survive if the entire thing freezes solid.