They stay very small so they can be kept in a 5 gallon tank their max size is 1 inch. But they are very aggressive and can be hard to care for. Your tank must be fully cycled before adding them and they really eat only live or fresh foods like snails, ghost shrimp, some small worms, sometimes they will eat frozen bloodworms or brine shrimp. But overall they are very picky. Also a general rule is you can have 1 for every 5 gallons of water.