The days of metal-framed tanks, sometimes with treated wooden sides are gone now and basically two types of tank are available to the aquarist, Acrylic (plastic) or glass tanks.

Acrylic tanks are lighter and cheaper than glass tanks, have few or no joins (therefore are less prone to leaks) and can be moulded in curved shapes. Acrylic also is clearer than glass. You may be aware of the green tint associated with glass.

The major drawback with an Acrylic tank is they scratch easily. Removing algae, although an easier task than on glass tanks, with a pot scrubber or a worn algae magnet is the most common cause of scratching. However, a fine haze may also appear on the walls over time due to abrasions caused by debris or sand being continually stirred up in the tank. Fortunately, minor scratches that are visible when an Acrylic tank is empty may disappear when the aquarium is filled. This is because Acrylic has a refractive index much closer to water than glass. Generally speaking though, Acrylic aquariums don't hold their shine as long as glass tanks.

Glass tanks, sealed with silicone cement, are more popular as they simply look good longer. They are however, by their nature, fragile so treat the aquarium with care. Glass is more resistant to scratching than Acrylic but once damaged, they are not easily repaired. Usually all but the deepest scratches in Acrylic can be carefully polished out but scratches on glass are normally there for life and they tend to be more visible.

Once you have chosen the material for your aquarium greater consideration should be given to its size and shape.

Broadly speaking the bigger the aquarium the better. Larger bodies of water are more biologically stable in terms of water chemistry and they are just as easy, if not easier, to maintain, as they require less water changes. Additionally, it is surprising how much space can be occupied furnishing the aquarium with rocks, wood and flourishing plants so extra volume is an advantage. (Aquariums measuring in excess of 36 x 18 x 18 inches or 50 US gallons are considered large).

Inevitably, there are practicalities to consider before purchasing a large aquarium. Do you have enough space? Can you reach the back of it for maintenance? Does your budget stretch to the larger filters, hood, lighting and heating requirements? Financial considerations may play a major part in the actual purchase of the tank itself but if this is a concern check the classifieds in the local newspaper. Unfortunately, many people leave this wonderful hobby and there are frequently aquariums offered for sale. It is worth remember that advertised prices are usually quite flexible and you may beable to afford a slightly larger aquarium after all.

Above all remember that the tank is a home for your fish and therefore should suit the needs of the species that you intend to keep. Choose a tank to suit the fish or vice versa. This way your fish will display their natural behaviour and you will gain more pleasure from them. Fast shoaling species such as Silver Sharks (Balantiocheilus melanopterus) will require a long tank, whereas a tall tank would be more suited to Angel Fish (Pterophyllum scalare). Territorial fish for instance many of the African Lake Cichlids, will require a tank large enough to accommodate their natural zones and provision should also be made for space occupied by the substrate, decor and plants. Clearly, in the wild some fish inhabit massive bodies such as lakes and large rivers and an aquarium that we would consider large may be claustophobic to the fish. Conversely, some fish inhabit small pools and dry seasons puddles are their home. In these cases small aquariums form the ideal habitat.

The volume of a tank does not necessarily dictate the number of fish it can accommodate. A long wide tank can be more beneficial to the health of fish as there is a greater surface area of water for good oxygen exchange. This may allow slightly more fish to be held, however the size of fish, their diet, type of filtration used, territorial needs and a number of other factors prevent a rule of stocking levels to be applied rigidly. For factors affecting stocking levels of an aquarium refer to this page.

Aquariums can be made to virtually any size but my advice is that unless a tank is destined for a particular space or display, it is best to stick to standard tank sizes. This will considerably reduce the cost when purchasing an accompanying stand or hood as these items will also need to be specially made to order.

If one intends to focus on plants in the aquarium, I recommend a tank no shorter than 48 inches (120cm) and no taller than 24 inches (60cm). The reason for this is to do with lighting. Plants require good lighting, around 2 Watts per gallon (but this is dependent on the plants that you intend to keep). The most popular means of lighting is by fluorescent tubes however; fluorescent tubes are not that powerful. An 18 inch tube is rated at just 15 Watts but 40 Watts can be obtained from a 42 inch tube, the size accommodated by a 48 inch hood. That's a full 10 Watts more than the next smallest size, which is just 6 inches shorter.

The 24 inch depth is about the maximum that one can get away with by lighting with florescent tubes. Beyond that depth, the only real lighting alternative is metal halide lamps and these are expensive in comparison. Most "background" plants will quickly reach the surface and after the addition of the substrate and accounting for filling the aquarium to around 1 inch below the brim this only affords some 19 inches of growing height. An aquarium 24 inches high is also the tallest tank that allows one to easily reach the back during maintenance.

Visual effect will also play a role in choosing your aquarium. Large aquariums can easily dominate a small room and space must be provisioned for comfortable viewing, equipment and manoeuvrability during maintenance. The way that we view a tank can have interesting effects on its size. Regardless of the size of aquarium, we tend to view them from only a few feet away. This means that when viewing aquariums measuring 60 inches or larger, the edges tend to be outside our field of view and thus give the impression of a much larger volume.

The height should be in good proportion to the length to prevent the tank from looking either "squashed" or "fat". As a guide good proportions are:

Aquarium Length	Aquarium Height
12 - 24 inches	12 -15 inches
24 - 36 inches	15 - 18 inches
36 - 48 inches	18 - 24 inches

As for width, once filled the aquarium background tends to advance making the tank look narrower. I therefore recommend that you purchase an aquarium measuring no less than 15 inches front to back. Wider tanks also afford a larger surface area, which is good for the fish and permits more space to accommodate the decor and to arrange the plants. Extra depth also allows for terracing to be constructed and with careful planting this will make the aquarium background recede. Although wide tanks are an advantage, avoid aquariums over 24 inches wide. These create the same limitations to reaching the back of the aquarium as tall tanks.

Standard tanks in the United States as sold by capacity in US Gallons and some tanks are designated L (long) or H (high). These are larger than the standard aquariums. Tanks in Europe are sold according to their dimensions in inches. European tanks are measured Length x Height x Width. For American consumers it is worth noting that a standard 55 gallon tank measures 48" long but only 13 inches wide. A wiser purchase, bearing in mind what has just been discussed, is the 75 gallon size.

To covert tank dimensions from inches to centimeters or to calculate the volume of an aquarium please visit this page.