I feed my turtles fish once a week. Of course, live goldfish are the closest thing to what they'd eat in nature. Second best I found was frozen smelt, because they have guts an bones.
When I couldn't find those, I once fed catfish. What a mess! Catfish are fatty fish, and they really messed up the water. I NEVER fed catfish again.
So, if not your pump, perhaps it's what you've been feeding them.