i agree with myo. even though the dwarf rainbowfish are smaller than other rainbowfish species they still need alot of swimming room. a 3 foot long aquarium or longer is best. a 20g long would be good. another thing to know before you buy rainbowfish is they need to be in groups of at least 6 and preferably larger groups of say 8-10. they also do best having 2 females to every male.