The Aquarium

(This article was first published in December 1992.)

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Of all the equipment used in the keeping of fish and other aquatic creatures, the most basic is the aquarium itself.  You can do without just about any of the paraphernalia usually considered indispensable – heaters, filters, lights, pumps, etc. – but you must keep your fish in something.  Any container that holds water for the purpose of keeping living aquatic organisms is an aquarium.

Of course, this is merely a semantic definition.  There are certain definite attributes we want in an aquarium, and tanks are manufactured to provide these.  Since setups differ (as do aquarists’ priorities), a wide variety of aquaria are available commercially, and many hobbyists build their own.  Here are some of the qualities that are important considerations in designing, building, and purchasing fish tanks:

            1. Must be watertight. ‘This almost goes without saying, but it is imperative that an aquarium be able to hold water indefinitely, without developing leaks, and without a catastrophic failure of materials that dumps its entire contents on your living room floor in seconds.

            2. Visibility.  The whole purpose of keeping a aquarium is to observe its inhabitants.  Pond fish (such as koi) are viewed from above, but an aquarium that is not merely a holding tank should provide distortion-free viewing from below the water line through at least one side.  (Most tanks, of course, can be viewed from three or four sides.)

            3. Materials.  Fish tanks can be made of a number of materials, but the most common are glass, acrylic plastic, and wood.  (A wooden tank must have a window of glass or plastic on at least one side.)  Each of these materials has advantages and disadvantages in terms of strength, weight, scratch resistance, transparency, durability, and cost.

            4. Size and Shape.  Aquaria are available in a wide variety of sizes and shapes, making them suitable for various aquaculture and decorative purposes.  Both size and shape affect the number and size of organisms that may be housed in a tank; they also affect the practicality of the tank in terms of locating, cleaning, and decorating it.

            5. Non-toxicity.  None of the materials used in the construction of the aquarium should be toxic or dangerous to aquatic organisms.  This rules out most metals and many paints and adhesives.

For many decades, the standard aquarium consisted of glass sides and a slate bottom held in a metal frame.  The material used to seal the panels in the frame and make them watertight was an asphalt-based, putty-like substance which was black in color.  It was quite flexible when applied, but it became brittle after hardening.  A tank assembled with this cement would often be watertight until it was moved, whereupon leaks would develop.

In the 1970s these tanks began to be replaced by all-glass aquaria, held together with plastic frames at the top an bottom and sealed with silicone cement.  The advantages of this construction are reduced weight and cost, improved durability, decreased incidence of leakage, and improved visibility because of the absence of vertical framing  members.  This is now the most common type of construction, although it was initially greeted with some skepticism.  In fact, early manufacturers of these tanks had to back them with warranties ranging from 5-10 years to convince aquarists to purchase them; they didn’t look as durable as metal-framed tanks!  Now that they have proven themselves and taken over the market, the typical warranty has dropped to 90 days.  (In general, if a tank hasn’t leaked within 90 days, it’s not going to leak unless it is abused.)

All-glass tanks are available in standard sizes ranging from 2½ gallons all the way up to 300 gallons.  Shapes include the conventional rectangular boxes in varying proportions, regular hexagons, and flat-back hexagons.  Although small tanks of this construction (up to approximately 30 gallons) are reasonably light in weight, mass increases rapidly with tank size.  Not only is more glass used in larger tanks, but it’s thicker, to resist the increases water pressure.  While a 10 gallon tank weighs only 11 lbs. and has glass 1/8" thick, a 55 gallon tank weighs 78 lbs.  Its glass is 5/16" thick.  A 150 gallon, with a glass thickness of 5/8", tips the scales at 358 lbs.!  When filled with water (at 8 1/3 lbs. per gallon), rocks, gravel, driftwood, etc., a 150 gallon tank may weigh in excess of 1800 lbs.!  Obviously it is necessary to support an aquarium on an appropriate stand; in addition, the placement of a larger tank should take into consideration the ability of the floor beneath it to support its mass!

In recent years, acrylic aquaria have been increasing in popularity.  Among their advantages are lighter weight than comparably-sized glass tanks, somewhat better visibility of the aquarium contents, and a far wider variety of commercially available shapes and designs.  All of these advantages are due to the characteristics of the acrylic material: it is less dense than glass and transmits more light; it can also be bent, molded, and shaped more readily.  Disadvantages: it’s more expensive than glass, and far easier to scratch.  You must be extremely careful when working with an acrylic aquarium in order to avoid scratching it.  Nevertheless, innovations such as built-in trickle filters and integral display stands have made these increasingly rapid sellers.

Wooden tanks, while not widely available commercially, are a popular choice for do-it-yourself aquarists who build them at home.  Wood is an easy material to work with, and is far less expensive than either glass or acrylic plastic.  For this reason, it is commonly used in the construction of larger aquaria, 100 gallons and up.  For example, a 150 gallon wood tank (72" ´ 18" ´ 28") can be built at a total cost of approximately $300.00.  This figure includes all materials: plywood, Plexiglas™ front (½" thick), adhesives, sealants, paint, etc.  A comparable glass or acrylic aquarium, purchased commercially, would cost in the neighborhood of $500.  In addition to the far lower cost of the wood tank, there is the advantage of customizing.  The aquarist can design and modify the aquarium any way desired; for example, to fit a given location, harmonize with a particular decor, or work with a specific filtration system.

If you decide to construct a homemade aquarium , it is important to ensure that the materials you select are non-toxic to fish.  This is especially true when it comes to chemicals such as glue, points, epoxies, and sealants.  Unless the product label specifically states “For Aquarium Use,” you should assume it is not until you have either contacted the manufacturer, discussed it with an aquarist who has already used the product safely with fish, or experimented on your own on a small scale.

The size of an aquarium should be determined by what you’re going to keep in it (large fish need large tanks), where you will keep it, how much it weighs, and how much it costs.  Keep in mind not only the cost of the tank but its accessories as well.  The shape of a tank should be influenced by its projected use.  For example, certain laterally-compressed fish, such as discus and angelfish, do well in deep tanks that allow room for full extension and display of their finnage.   The breeding of some species of fish, such as bettas and certain catfish, may be more successful in a shallower tank.  Fish that swim constantly (such as arowanas) or rapidly (such as tinfoil barbs) do best in a aquarium long enough to indulge these propensities.

Another concern in selecting a tank’s shape and size is the water surface area.  In an aquarium with no artificially-induced water circulation, the surface area alone determines the carrying capacity of the tank.  The use of aeration and powered water movement reduces the importance of surface area relative to tank volume, but there are certain extreme conditions under which surface area remains a limiting factor  One such extreme is the column-shaped aquarium, which may hold as much water as a normally -shaped tank with only a fraction of the surface area.  Without a vigorous circulation to pull water from the bottom of the tank to the top to permit gas exchange, such an aquarium is unlikely to have sufficient surface area to maintain a uniform level of dissolved oxygen.  This severely limits the number and size of fish that can be housed therein.

It’s obvious that the selection of an aquarium should not be a random process, but should be made with careful planning and forethought.  Decide what you want to deep in it, where you will put it, and how much you can spend on it (including its occupants and accessories).  This will help you choose the appropriate shape and construction, and soon all of the pieces will fall into place.  Prudent consideration at this stage will make the entire process of aquarium setup simpler and more efficient, which will, in turn, make owning and maintaining it more enjoyable.