Basking on sunny rocks and logs in nature helps a turtle produce vitamin D3 required to metabolize calcium for a strong shell and other nutrients vital to his health. In the home aquarium artificial UV light provides the same benefits. Too little UV exposure results in metabolic bone disease, stunted shell growth and premature death. Your turtle will get adequate UV light if you leave the light on 10 to 12 hours per day.
Catching Some Rays
UV light consists of both UVA and UVB rays. While UVA rays help your turtle maintain feeding, breeding and activity, it is the UVB light that is crucial to processing nutrients. UVB light does not penetrate glass, so setting your turtle in a sunny window will not provide the full spectrum he needs. Hang your UV light 12 to 15 inches above the top of your turtle's shell. A bulb emitting 3 to 5 percent UVB left on for 10 hours a day will decrease in UVB output after about 10 months. Plan to replace your bulb annually at a bare minimum.
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