Hi,
Crocs and turtles can sometimes be kept in the same enclosure successfully without much problems. I wouldnt keep Red Eared Sliders with them as they are notoriously obnoxious turtles which like to bite toes. I have an Eastern Painted which is fine with crocs however, he gets chased by my gators. I personally wouldn't recommend keeping them together unless you have a spacious enclosure for stress factors. I dont' keep my turtles housed with my crocs all the time, as they usually are only with them when they are in their outdoor enclosure. You can experiment and see what happens but if you see the turtle try to bite toes or tail at any time, I would recommend separating them immediately.
JMO,
Chris
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Chris Law
U.A.P.P.E.A.L. (Uniting a Proactive Primate and Exotic Animal League)
Herpetoculture Element Representative