Abstract: A pump transfers water from an aquarium into a top container and an overflow container that are inserted into an aquarium, lowering the water level within the aquarium, and thereby creating the effect of a tide pool at low tide. Water is pumped into the overflow container when the top container is filled, while drainage holes in the overflow container continue to allow some of the water to flow back into the aquarium. As the overflow container fills with water, its increasing weight pulls down a lever connected to a flapper, uncovering a drain in the top container, thereby draining water pumped into the top container through the drain, and completely draining the overflow container, in turn raising the water level in the aquarium, thereby creating the effect of a tide pool at high tide. When the overflow container is completely drained, the lever is raised, closing the drain, and the cycle is repeated.