Red-eared sliders and other aquatic turtles often develop respiratory infections as a combination of husbandry errors such as cold water, a basking site that isn't warm enough, a poor diet, and lack of ultraviolet-B light.

The signs of a respiratory infection may be subtle, such as an occasional bubbles of mucus from the nostrils or even some bubbles around the eyes.  As the infection progresses and become pneumonia, the turtle may float oddly in the water, listing to one side or being unable to submerge.  In some cases the turtle may sink and struggle to get back to the surface of the water.  The red-eared slider may extend its neck far forward and open its mouth as it gulps for air.  Prescription antibiotics are necessary to treat these life threatening infections. Whenever you see any of these signs, you should set up a consultation with a veterinarian.

In the meantime, warm the water temperature to 80 to 85F.  Make sure the basking spot has a nice white spotlight that heats the area to 90-95F for 12 hrs a day.  Put an ultraviolet-B emitting bulb, such as a Zoomed Reptisun 5.0 or a Powersun, over the enclosure and make sure it is on for at least 8 hrs a day.  Feed a good quality pellet designed for aquatic turtles, or a mix of trout chow, koi pellets, and earthworms.  Fresh green leafy produce, chopped whole fish, and even chopped baby mice help round out a good diet