I had purchased a couple these heaters, they look kinda like flex wat, very thin pads with no regulating knob or anything. If anyone knows what i am talking about maybe you can answer my question. Now that i have it i was reading the directions and it sais only use on glass tanks, im guesing they say this because it stick to the bottom of the tank. I am useing tubs. Do i have to stick it on to the buttom, cant i just place it under the tub and use it that way? though i dont know which side the heat will come from and i dont want to mess it up...any help would be greatly appreciated.