Largest freshwater turtle, the record weight is over 300 lbs. That said, I don't think I've ever owned a more sedentary animal. Most people keep them in plastic or steel tubs when the exceed 12".
i took out rocksteadys small pebbels like that, because he kept eating them... i switched to big river stones. but then his feeder fish would hide in them. so i switched to sand and he loves it! he shakes his little ass and burys himself in the sand its funny...