Red-Eared Slider Water Temp – What’s The Ideal Temperature

Red-eared sliders are cold-blooded animals. That means they depend on the external environmental temperatures to keep warm. If the water temperature is too cold, your red-eared sliders will go out of the water to look for a place to bask. If the basking spot is also cold, the turtle may become lethargic, brumate, or even die.

Therefore, the ideal water temperature for a red-eared slider turtle is between 72°F and 76°F. On the other hand, your turtle’s basking area temperature should be between 85°F and 90°F. If the water and basking area temperatures are hotter, your turtles will burn. Use artificial heat sources like UVB that produce at least 5 to 10% UV-b rays.

Adequate UVB light discourages metabolic diseases and shell problems in red-eared sliders. Although natural sunlight is a good thermoregulator, avoid placing your turtle tank in direct sunlight. Allow the red-eared sliders to bask in the sun at will. I have discussed everything you need to know about the ideal temperature of the red-eared sliders below.

What is the ideal Red-eared slider water temperature?

Red-Eared Slider water temperature

The ideal water temperature for red-eared sliders is between 72°F to 76°F. At that temperature, the turtle’s metabolic activity will be optimal. Instead of being sluggish and lethargic, you will notice increased eating, playing, and mating activity.

The ideal water temperature also promotes optimal heart rate in turtles. You can use a veterinary stethoscope to listen to your red-eared slider’s heartbeat. On average, the red-eared slider’s heart rate is 25 times per minute from 72°F to 76°F. 

Note that red-eared sliders are ectothermic. Although the turtle spends most of its time in the water, it occasionally comes out to bask. Therefore, you should provide the turtle with a basking area near the turtle tank. Ensure the basking spot temperature is 85°F to 90°F.

However, red-eared slider hatchlings and sick red-eared sliders need slightly warmer temperatures than healthy turtles. Experts recommend a temperature of 78°F to 82°F for the vulnerable turtles. It will keep them from getting respiratory infections and brumation. 

At night, the red-sliders water temperature should not fall below 65°F. I will explain later how to measure the water temperature of a red-eared slider. You will also learn how to heat their water to give the turtles an ideal temperature that does not burn them or trigger brumation.

What water temperature is too hot for a Red-eared slider

A red-eared slider water temperature above 80°F is too hot for the turtle. If the water temperature is that high, bacteria will multiply rapidly in your turtle tank. Even worse, dissolved oxygen will diminish and render the water inhabitable.

If your red-eared turtles are coming out of the tank and not getting back into it, the water temperature might be too hot. Similarly, the basking area could also be unbearable for your red-eared sliders if the temperatures rose above 90°F.

A basking area that’s too hot will burn your turtles and keep them submerged throughout the day. Lack of basking encourages fungal and bacterial infections in red-eared sliders, and it can also result in health problems like shell rot.

Here are some things that will happen to your turtle if the water is too hot:

  • Bacterial and fungal infections such as shell rot
  • Overheating and burns
  • Hyperactivity

What water temperature is too cold for a Red-eared slider

A water temperature between 50°F to 72°F or lower is too cold for a red-eared slider. Keeping your turtle at these cold temperatures for extended durations can lower its metabolism significantly. 

Low metabolism means the red-eared slider will be inactive to reduce energy consumption. Although the turtle might eat, it will not move around the tank so often. It will also defecate less often.

If the red-eared turtle’s metabolic rate falls by 80%, it will undergo brumation. That is a cool-down strategy to survive the lower temperatures. For weeks, they will be sluggish or play dead in a corner in the turtle tank. 

However, if a warmer area is next to the cold water, your turtles will occasionally come out to bask. If they reject the water and tend to bask most of the time, measure the water temperature and raise it or lower it accordingly.

Here are some things that will happen to your red-eared slider if the water temperature is too low:

  • Respiratory infections
  • Failure to defecate
  • Eating without drinking water
  • Low metabolism
  • Reduced heartbeat
  • Brumation
  • Death

Do red-eared sliders need heated water?

Of course, you need to heat the water for your red-eared sliders, especially in the winter. You can also heat the water if your room temperature is below 50°F to enhance the turtle’s metabolism and keep them healthy and happy.

But how is it done? How can you heat your turtle’s water? Well, there are many ways to do it. First, I recommend a submersible water heater like the SunGrow Turtle and Frog Heater. It is an affordable and efficient way to restore normalcy in your turtle tank. 

However, note that the size of the submersible heater depends should be relative to your tank size. For a 50-gallon turtle tank or larger, use a much larger heater. 

Secondly, install artificial UVA or UVB light such as the adjustable Reptile Heat Lamp over your turtle tank. Although it won’t increase the water temperature much, the light bulbs will increase the warmth in the basking area. 

Ensure the UVB light rays are rated between 5 to 10% to improve your turtle’s calcium metabolism, appetite, and heart rate. Adequate UVB light is also essential for lowering algae in your aquarium. In the next section, you will learn how to measure the water temperature.

How to measure the water temperature of a red-eared slider

There are several ways to measure the water temperature of a red-eared slider:

  • Infrared thermometer: An infrared thermometer temperature gun is more effective because you don’t have to submerge it in the water. It uses a laser and shows the readings on a clear screen. Besides, it can measure the temperature of the red-eared slider with significant precision. 
  • Stick-on thermometer: It is an easy and convenient way to measure the aquarium water temperature. As the name suggests, stick it on your turtle tank’s side. The best stick-on thermometer for red-eared sliders is the hygger Stick-on Digital Aquarium Thermometer.
  • Analog thermometer: Although digital thermometers are best for measuring the water temperature of red-eared sliders, analog thermometers will also give correct values. Not only are they cheap, but they are also relatively easy to use. 

Signs that your red-eared slider’s water temperature needs adjustment

Here are some signs that your red-eared slider water temperature needs adjusting:

  • Mold is growing on your turtle’s shell: The primary cause of increased mold in the aquarium is high temperature. It encourages bacterial and fungal build-up, increasing your turtle’s vulnerability to shell rot.
  • Your red-eared turtle is lethargic: Lethargy means that your red-eared slider is not active or interactive as usual. Perhaps the turtle is barely moving, eating, or swimming. These signs reveal a water temperature problem.
  • The turtle basks more than it swims: Red-eared sliders like swimming. They spend most of their time in water and come out of the water once in a while. However, if the turtle basks for extended periods and dislikes the water, monitor the temperature and adjust it to 72°F to 76°F.
  • The red-eared slider is not moving for days: When its metabolism goes down by more than 80% due to cold water, the turtle will act dead for days or weeks. It does this to withstand the cold and minimize energy consumption. Adjust the water temperature if the turtle does not move.


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