The Right Fish Tank

The general rule is to buy the largest aquarium you can afford and can accommodate in your home. The reason for this is fairly straightforward: Fish require adequate space to swim and sufficient oxygen to live; both are dictated by the size of the tank. The oxygen content of water is related to the surface area of the tank and the temperature of the water. Warmer water has less oxygen than colder water. Since most freshwater tropical fish prefer water warmer than 75 degrees Fahrenheit, the amount of oxygen in the tank may be limited. The more surface area a tank has, the more room for gas exchange at the surface more opportunity for oxygen to enter the water and toxic gases to leave. Therefore, the larger the surface area of the tank, the more fish the tank can hold.

Several different methods have been used to determine fish capacity, and there are several general rules. In my opinion, it is better to err on the side of too few fish than too many fish. Most aquarium enthusiasts use fish length and tank volume to estimate the number of fish an aquarium can hold; larger fish consume more oxygen and, therefore, require more aquarium space. The general rule is 1 inch of fish per 4 gallons of water for the first six months. You can gradually increase fish density to 1 inch per 2 gallons after this initial period. For example, a 40-gallon aquarium should contain no more than 10 inches of fish for the first six months. These may comprise ten 1-inch Neon Tetras or five 2-inch Oscars. After six months, additional fish may be added gradually to increase the total number of inches to 20.

Keep in mind, however, that fish grow, and your 2-inch Oscar may be 3 inches after those six months. Also, realize that this general rule does not compensate for the shape of the fish. The width of a fish is called its girth. The girth of an Eel is much smaller than that of an Oscar, and the 3-inch Eel is likely to require less space than the 3-inch Oscar, so the general capacity rule does not apply. If you plan to keep heavier fish (fish with a greater girth), be more conservative in your tank capacity calculations.

Because surface area is so important to the capacity and health of your aquarium, long tanks are much better than tall tanks. Even though both tanks may hold the same volume of water, the upright (tall) tank has much lower carrying capacity of fish because of its smaller surface area.

Once you have decided on the appropriate size of your aquarium, choosing the tank itself is very straightforward. Home aquariums are made of rectangular glass plates sealed with a silicone rubber cement, or of molded acrylic; both have their ups and downs. Glass aquariums are the most common and practical aquariums to buy, and I recommend them for the beginner. They are built for the sole purpose of housing living animals and are, therefore, nontoxic. Glass does not scratch as easily or yellow as acrylic does.

Aquariums with plastic or metal frames are sometimes available, but I have found that this design is not as aesthetically pleasing and that the frames are unnecessary. When choosing your tank, be sure there are no scratches on the glass and that there are no gaps in the silicone that can cause leaks.