CLOSED-LOOP ECOSYSTEM. This 3-gallon fish tank is a closed-loop, self-cleaning ecosystem. Using the science of aquaponics, the fish waste naturally fertilizes the plants above, and the plants, in turn, clean the water for the fish. Great for small pet fish and growing fresh herbs above. INCLUDES: 3-gallon tank, water pump, all-natural aquatic supplies, organic seeds, 5 grow pots, fish food, and a coupon for a 99 cent Betta fish from Petco.