Your next concern is choosing aquarium dimensions, which includes both the size and shape of the aquarium.
Ideally, you want to purchase the largest tank possible -- one that you can afford and that will fit into the chosen space. A larger aquarium will hold more fish, of course, but greater size will also provide a more stable aquatic environment.
As the volume of water increases, it can be easier to maintain consistent water temperatures and good water quality. This is not to imply, however, that a modest-size tank will have problems. With a little care and attention, any tank of 10 gallons or more can be a healthy home for fish.
The cost of an aquarium rises moderately with its size until you pass capacities of about 55 gallons, at which point prices rise much faster. The amount of glass needed for very large tanks and the increased thickness required as the tanks become deeper contribute to these price increases.
The numbers and sizes of fish that can be kept are affected by both the tank size and the tank dimensions. For this reason, it may help to know what kinds of fish you want to keep when shopping for an aquarium.
If you don't want to plan that far in advance, just be aware that you may have to avoid certain types of fish if your aquarium is not suitable for them. Don't worry, though; no matter what kind of tank you buy, you'll be able to choose from a great variety of potential residents.
You will discover that aquariums of similar or identical capacities can have very different dimensions. While the amount of water that an aquarium holds is important, many new hobbyists do not realize that the dimensions of a tank can be important, too.
The length and width of the tank determine the surface area of the water, and surface area directly affects the number and size of fish that can be kept in the aquarium. The significance of surface area may not be clear until you understand a little more about the biology of an aquatic environment.
One of the most important rules of successful fishkeeping is to not overstock your tank. Overcrowding can make it all but impossible to keep fish alive and healthy.
Increasing the filter size and the amount of maintenance can partially compensate for too many fish, but in the long run nature takes it course and fish will sicken and die until the aquarium is no longer overcrowded.
Exactly what constitutes overcrowding, however, is hard to say. Looking at the tanks in stores is no help because these aquariums are vastly overstocked. The short amount of time the fish are in these tanks, combined with extensive filtration and frequent maintenance, allows retailers to maintain heavy tank populations.
Learn more about choosing an aquarium size in our final section.