I doubt it would stunt growth, that's like saying using hand lotion will stunt a human's growth hahaha. I use it twice a week on my tortoise, which seems to keep his shell nicely moisturized and healthy (don't know about positive health benefits, but his shell starts to look dry without it). Every once in a while when I have my turtles (an RES and a diamond back terrapin) outside for some exercise for a few hours I will put it on their shells so it has a chance to dry before going back in the water. Haven't noticed much difference in them. It won't hurt, but I don't think it's necessary provided they have a good diet, proper lighting, a basking area and clean water.