Jordan D. Jonas/ Colorful Marine Fishes Inside An Aquarium

The aquarium you choose will be the whole world for the fish you keep, so buy the biggest you can afford and have room for. Some fish may require more space than you might realize -- for instance, common goldfish require at least 20 gallons per fish and fancy goldfish require 10 gallons per fish. Find out the space requirements for any fish that you'll be keeping and follow them. However, remember that the minimum space requirements are just that -- minimums. If you can buy a tank larger than the minimum, do so for the comfort and health of your fish.