Instructions
Let your tank sit for a few days after everything is ready in order to make sure the water is at the right temperature and everything is working properly before you add fish.
Visit your pet store and look at the variety of fish they have. They are usually grouped in categories such as community fish, aggressive fish, semi aggressive fish, goldfish and feeder fish.
Decide on the type of fish you want to get to populate your tank. Community fish are the best way to go--there are many varieties and they come in many sizes.
Check the tags that are on the tanks to see the size the fish grow to. Since community fish need to be in schools of at least three, you don't want to buy fish that are going to grow too large. The rule of thumb is one inch of fish for every gallon of water. Therefore, if you have a 10-gallon fish tank and the fish you buy can grow to an inch then you only want to buy 10 fish.
Start with tetras or danios, since they are the easiest to keep. Some of them can grow quite large so check this before you buy them. Live bearing fish, such as swordfish and mollies are also good fish to start with and they have baby fish--other fish just lay eggs. Therefore, you can populate your tank by just having male and female swordfish or mollies.
Buy the fish of your choice and take them home. You need to put them in your tank in the bags for at least 15 minutes so they can get used to the new water while still in the water they are accustomed to. Cut the bags and let the fish free to swim.
How to Buy the Right Fish for a Small Tank
You've decided to set up an aquarium. First, you need to buy the tank. Start with a small tank, five to 20 gallons. After you buy the other equipment you need to put your tank together. Once your filter, decorations, air pump and a heater are assembled you are ready to buy the right fish for your small tank.