Heating Your Aquatic Turtle Habitat
There are three things that all aquatic turtles absolutely must have: Heat, light, and clean water. These are matters of survival for turtles. Without those three things, your turtle will die.
Making sure that your turtle habitat is properly heated isn't a choice. It's an absolute requirement if you are going to keep turtles. Like all reptiles, turtles are ectothermic (what we used to call "cold-blooded") animals. That means they can't control their body temperatures. Their environment determines their body temperatures.
To be healthy and happy, turtles need their body temperatures to remain within a fairly narrow range. Creating that temperature range is one of the most important things that we do for our turtles. In fact, their lives depend on it. Luckily, heating your turtle's habitat is actually pretty easy to do, once you know how.
The first thing you need to know is what kind of temperatures your particular turtle specie likes. You can find this out by looking at the care sheet for the specie of turtle that you have or that you plan to have. Austin's Turtle Page is a great resource for all kinds of information about turtle care, and they have a whole section devoted to care sheets for different kinds of turtles. So check out the care sheet for your kind of turtle to see what kind of air and water temps it likes.
Maintaining Turtle Tank Temperatures
There are two temperature ranges that we have to maintain in our turtles' habitats: The air temperatures and the water temperature.
Although these vary according to species, in general most adult aquatic turtles like a water temperature in the high 70's Fahrenheit, and an air temperature in the mid 80's Fahrenheit. Baby turtles usually need slightly higher temperatures. My baby Southern Painted Turtles, for example, like 82 degrees Fahrenheit water temperature and 90 degrees air temperature. As they get older, I'll gradually lower the temperatures to what they need as adults.
In addition, turtles who are sick need higher temperatures than turtles who are well. Because turtles are ectothermic animals, they can't run a fever when they're sick; so we have to raise their habitat temperatures a little to do that for them. In general, a sick turtle's air and water temperatures should be raised about four or five degrees Fahrenheit from it's normal preferred temperature.
Regulating Water Temperature in a Turtle Habitat
The easiest way to maintain the correct water temperature in a turtle tank is by using water heaters. These are commonly available in pet supply stores, but you have to be careful to choose the right heater.
My favorite heaters for turtle tanks are the Marineland Stealth Pro heaters, like the one in the picture on the right. They are unbreakable, adjustable, and available in several wattages for different size tanks. They also have a light on them to tell you whether they're working or not (but I always use stick-on thermometers on the outside of the tank to monitor the water temperatures, anyway).
Because heat is so important to turtles, I like to use two water heaters in my turtle tanks. This way if one of them stops working, the water won't get too cold before I realize the problem and replace the failed heater. A failed water heater is less obvious than a blown-out light bulb, so I like to have a second heater as backup.
Many heaters made for fish tanks are made of glass. Glass heaters are no good for turtle tanks because turtles are heavier and rougher than fish, and may break a glass heater. Some heaters claim to be made of "shatterproof glass," but I don't trust them.
Water heaters made for reptile tanks that are enclosed in a plastic housing are okay safety-wise, but most of them are pre-set to a specific temperature, usually around 78 degrees Fahrenheit. That's fine for healthy adult turtles, but I like to be able to set the temperature myself because I also keep baby turtles (who need warmer water), and because I want to be able to raise the temperature if my adult turtles become ill.
Regulating Air Temperature in a Turtle Habitat
Most turtle habitats use the basking lamp to regulate the air temperature. It is placed at a distance and position that heats the basking area to the correct temperature range for the turtle.
Notice that I keep talking about the air temperature range. What I mean by that is that your turtle's habitat shouldn't all be the same temperature. Instead, the temperatures on the basking area should range from the low end of your turtle's comfort range to the high end.
This is actually easy to do: Adjust the basking spotlight so that the temperature right where it hits the basking area is at the high end of the temperature range. As the turtle moves farther away from that spot, the temperature will drop a little. The turtle will decide where it feels best.
If you have a big enough habitat, you can install two basking areas, with slightly different temperatures on each one.
Unlike the water heaters, which have thermostats and always maintain the right temperatures when they are working properly, the air temperatures will vary depending on how warm or cold the air in the room is. We can make minor adjustments by moving the lamps a little bit closer to the basking area to raise the temperature, or a lit bit farther away to lower the temperature. It's important to check the thermometers regularly to make sure the temperatures are where they should be.
Other Heat-Related Equipment
Thermometers are essential for all turtle habitats. We need at least two: One to measure the temperature at the basking area, and one to measure the water temperature.
I personally like stick-on LCD thermometers. The water thermometer gets stuck outside the tank so the water is behind it, and the air thermometer gets stuck to the inside of the tank (above the water line) near the basking area. I like these thermometers because they're accurate, easy to read (especially for us older folks), they can't break like glass thermometers, and they're cheap.
Make sure the air temperature thermometer is a "high-range" one that can display temperatures at least into the high 90's F. Thermometers made for fish tanks typically don't display temps much about 80 F.
Heat emitters screw into an ordinary light socket, but produce little or no visible light. But they generate a lot of heat. They're usually not necessary unless the room the habitat is in is very cold. Be very careful when using them. If they are placed too close, they will burn your turtle.
Under-Tank Heaters, Rock Heaters, etc.
Most pet supply stores sell a wide variety of heaters that fit under a tank, or which are shaped liked rocks and go inside the tank. I don't recommend any of them. They're really designed for terrestrial reptiles, not aquatic turtles. In addition, the under-tank heaters are expensive and don't do a good job regulating water temperatures, and the rock heaters may burn your turtle's feet or plastron (the underside of its shell). They're designed for desert animals, not aquatic turtles.
So don't waste your money on stuff like that. Buy good-quality lights and water heaters instead, and use a heat emitter if you still need to raise the temperature a few degrees.