It really depends on which species you want to keep. Some tropical fish, such as Bettas, like small tanks while others prefer much larger aquariums kits. The Fluval Edge is one of the best fish tanks for small tropical and marine species since it comes with a heater, light, and integrated filtration. If you want to keep tropical fish that require a large aquarium you can go for Fluval Flex 32.5 gallons. This tank has a powerful Marine 3.0 LED light which is ideal if you want to grow corals.