I have the same problem, my turtle poops on the basking sopt instead of the water. Kinda aggrivating cuse that means there is now reason for my filter which i hade to spend money on. instead i have to scrub off the poop with a toothbrush.
I just wanted to make sure that it didn't mean sickness or anything! I'm starting to get paranoid about every little move they make! It was one thing when we FOUND wild turts that we spent little to no money on, but now that we've paid for BOTH the turts AND the equipment, I'm afraid my husband would have a heartattack if these little one's died or something!