I have a 6 inch long yellow bellied cooter in a 75 gallon long tank. He's in there now with a dozen small guppies, but I was wondering if there are any kinds of catfish or other medium sized fish that would help keep the tank clean (and him company) without being devoured. Also, would a crayfish do good in a turtle tank??? The water temperature is from 70-72 degrees in the tank.

Thanks alot!