ive head and seen the end results of this. It tends to end up with a dead (if not eaten attacked and killed) frog. Also frogs tend to prefer shallower water and cooler temperatures (and cooler water) than turtles they don't bask like turtles and prefer to hide in damp cool places where turtles like warm sun drenched places. You can provide the environmental niches needed for both species in a tank at home. If you make a frog live like a turtle it will cause stress and illness. Also there the chance of disease and bacteria incompatibility as well. Its just not worth the risks