I have a red eared slider that is not eating and only basking please help?

I have 2 small red eared slider turtles, one of them is feasting while the other did not eat today. He ate yesterday but he is only basking. My water temperature is between 77-78 degrees. I realized i may feed them too much shrimp :S But sometimes i feed them the turtle pellets. I put like 10 pieces of shrimp in the tank and let them help themselves eat it. But I am scared the turtle not eating will die! What do i do?