Rings left in the bathtub are often caused by hard water. You can add 1/2 cut of baking soda to the bath for about every 15 gallons of water to soften the water and keep the rings from forming. Rinsing the tub with a few cups of water and spraying with "Clean Shower" or other after shower spray after the bath has drained will increase the amount of time between needed cleanings.
