Top Fin® Half Moon Aquarium - 3.5 Gallon. Create an enchanted aquatic environment with the Top Fin® Half Moon Aquarium. This sturdy, 3.5 US Gallon plastic tank measures 12.2" L x 8.3" W x 12.3" H and is ideal for small fish. The set includes a Top Fin "Element" filter, two filter cartridges, and a hood featuring a single LED light and a convenient feeding door. To ensure a healthy habitat, place the aquarium on a stable surface, condition the water properly, and allow the water to cycle for four hours before introducing your fish.