Welcome Pearl --- nice tank I do recommend getting a digital probe thermometer and if the screen on your tank is a fine mesh like a screen door please move the UVB inside the tank -- the screen blocks approx 30% of the UVB rays --- if the screen is a wide hole type it can stay on top but your basking decor piece needs to be 8-10 inches directly below --- if inside the tank please have the distance directly below 12-15 inches