Aquariums

The standard aquarium is a rectangular prism, but there are many alternatives available. Here are some major considerations:

Aquarium Shapes

Surface area is where gas exchange (oxygen in, carbon dioxide out) takes place, and the bottom is where many territorial fish set up their home turfs. Often the more decorative aquarium shapes have relatively low surface area. Good water movement and filtration can make up for poor surface area, and restricting the livestock to non-territorial species makes bottom area less significant, but in general, a longer, lower aquarium can sustain more life than a narrower, deeper tank can.
Very deep tanks are harder to service. Just scraping the algae off the glass of a 6-foot tall aquarium requires considerable ingenuity. Siphon vacuuming the gravel is another considerable challenge.

Choosing the right Aquarium Size

Standard sizes range from 2½ gallons to 240 gallons, and custom sizes are available from less than a gallon to thousands of gallons and even larger.
Get the largest aquarium you can possibly manage. It is easier to care for a large aquarium than a small one, and it is much easier to care for a huge aquarium than a tiny one. The reason is simple: maintaining a fish tank is in large part a matter of keeping a complex system in balance; the more water there is, the longer it takes for an imbalance to occur.
Aquariums are heavy, and water is even heavier. For a final weight of tank, stand, gravel, and water, figure about 10 pounds per gallon (1.2 kilos per liter) of the setup. You must use a stand or cabinet that is specifically designed to hold an aquarium of that size, and you must be certain that the floor under the stand is able to support the weight without problem.

Desktop Tanks

Desktop tanks include the popular nano systems, as well as a great range of aquariums, from ornate betta bowls to art-deco sculpted tanks with miniature lighting and filtration options. But they must be properly utilized; you cannot simply scale down a regular aquarium setup to fit a tiny desktop unit.
Small displays are perfect for animals and plants that would be lost in even typical small tanks. Small invertebrates like shrimp—both freshwater and marine—are great for these little tanks. Tiny fish like Heterandria, Boraras, and the smallest gobies can be the focus of the display instead of just being lost in the background…or eaten for lunch! So instead of a lone zebra danio endlessly switching directions or a stunted community of regular aquarium species, a school of truly tiny fish can explore a planted landscape in which they are the main attraction.
Water stability is extremely precarious with these small volumes—another reason to use only the smallest livestock. Heating, lighting, and filtration become major issues as well, but manufacturers are rising to the challenge and producing equipment designed specifically for these diminutive aquariums.

Aquarium Setup Advice

There are many factors which determine the proper aquarium for a given application. Many of these factors are aesthetic, and therefore up to you to decide. Factors outside your preferences include the size and type of fish you wish to keep and your purpose for the setup—ornamental display, breeding, etc. So remember:

Overcrowding is always bad, and often it ends in tragedy. There is a terrible tendency among hobbyists to squeeze too many too-large fish into a tank.
Stock wisely. A 150-gallon tank is too small for a single 2-foot arowana, but it could easily house a thriving community of 200 or more Heterandria formosa! Likewise, you could keep a collection of a half-dozen Central American cichlids in a 55-gallon tank, but if two of the fish are a pair and they spawn, the other four cichlids would need to be removed.

So, weigh the factors, make your choices, and get the perfect aquarium for your wants and needs. The enormous variety of aquariums on the market just about guarantees there are several that will work well for you.

Glass versus Acrylic Tanks

This is pretty much a matter of individual choice, as both types of tanks have their advantages. In general, acrylic tanks are stronger, resist breaks and leakage, offer better thermal insulation, and are clearer, lighter, and easier to move. The biggest drawback to acrylic is that it can be scratched, so attempting to clean the algae off with a razor blade is not an option. Special care must be taken in cleaning the tank, using nonabrasive cleaning pads and scraping tough algae growth with a sharp-edged plastic instrument.

Glass is less expensive, and it is available in a variety of shapes and sizes, but it can’t be contoured to some of the shapes that can be done with acrylic tanks. They don't scratch as easily as acrylic tanks, but glass tanks don’t hold their value as well as those of acrylic. Nevertheless, they seemingly can last forever, as many of my glass tanks are nearly 50 years old.