Instructions
Set up, condition and stabilize your brand new tank properly. You cannot fill a tank with tap water and put expensive fish into it. Ask a reputable pet store or long time aquarium owner how to set up, condition and stabilize a new tank before you buy fish.
Know your species. When you get to the store, you'll find both saltwater and freshwater fish in aggressive and non-aggressive varieties. You're searching for freshwater, non-aggressive fish only. Saltwater tanks are not for beginners, and freshwater aggressives kill defenseless fish. Take a fish-savvy friend with you to shop.
Buy healthy fish. Fish shouldn't appear "roughed up" or have wounds of any kind. They shouldn't have white spots on their fins, have a black coating or be hunched into a question-mark shape. If any fish appear ill, leave that tank alone.
Purchase small schools for your non-aggressive aquarium. If it swims in a school, it needs to live in a school. Don't buy just one or two schooling fish, buy at least a dozen.
Take home a couple of small pleccos (side suckers). Yes, they're ugly. Yes, you need them. A large plecco won't harm smaller fish, but large pleccos are expensive. Refrain from buying expensive fish until your tank stabilizes completely.
Purchase a small number of inexpensive, non-aggressive fish. No more than one quarter of the amount you eventually want in your tank. Tanks take time to stabilize, so be prepared for some of them to die. Double-check before leaving the store that you've purchased compatible fish.
How to Buy Fish for a Non-Aggressive Freshwater Aquarium
Freshwater, non-aggressive aquariums are ideal for those new to keeping fish. Non-aggressives typically won't harm one another, unless one of them is ill, which makes these aquariums easier and less expensive to keep than their predatory counterparts. Many species also run in school formation, beautifully enhancing the look of the tank.