I kept a Mud turtle in a 29g fish tank for 4 years. With no UV. I didn't know any better at the time. I found it as a hatchling and threw it in the tank. It lived with my fish and ate fishfood. If a fish got sick, it was turtle food. If having no UV affected it's health, you couldn't tell. I have also seen snappers and muds basking at the edge of pond shallows wuth just their shell protruding from the water. So they will bask when the urge strikes them. My mud never left the water, ever. If you feel like you're compromising your turtles health without the UV, then get the bulb. Checker.