When you are on a business trip or traveling, use our water compensator to avoid water shortage in your fish tank, aquarium tank, tortoise tank, or other tanks. Better than a float valve, no wiring or power required, takes less space. It very easy to use, practical and interesting. Simply screw the compensator onto the water bottle and stick it to the water tank. When the water level drops to reveal the shorter tube, the water in the bottle automatically flows into the tank due to pressure difference. Screw-free, no damage to the tanks. Made of corrosion-resistant ABS material, which is also usable in saltwater.