RES tend to munch on about everything in their tank. I'm not sure what your basking platform is made of but if the turtle(s) continue to take chunks off I would consider getting a new platform that they can't tear apart.
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0.1.0 Colombian Red-tailed Boa (100% Het. for albino)
0.0.2 Western Hognose Snakes
0.2.1 Plains Garter Snakes
1.0.0 Red-sided Garter Snake
1.2.0 Barred Tiger Salamanders
0.0.1 Red-eared Slider
0.0.1 Common Snapping Turtle