The aquarium is probably the single most important and expensive purchase made by the aquarist. It is very important the tank meets all the quality controls.
  There are several main criteria to keep in mind -

Volume/Surface Area Ratio -
The aquarium must have enough surface area to exchange carbon dioxide for life going oxygen. Small tanks are convenient, but they present a number of difficulties for the marine hobbyist. Creatures of the coral reef are reliant on stability of their environment and have adapted to predictable conditions over the past years. Larger tanks offer for more stability in terms of PH and temperature than small tanks.

Unnatural territories -
Vast amounts of marine fish are territorial and nearly always protect a horizontal area. Choosing a tall, than tank is likely to bring in inhabitants into unnaturally close contact and may lead to territorial disputes, whilst the more dominant  species try to establish their boundaries.

Choosing a shape -
An aquarium of irregular shape is generally subject to viewing distortion. Livestock can appear to become split between two or more pieces of glass or acrylic - leaving the aquarist frustrated.
  Most aquarists choose the traditional rectangular design as the potential problems are more easily overcome.
 
RECTANGLULAR SHAPE                                              IRREGULAR SHAPE

Stands and safety-
The total contents of a fully stocked aquarium is extremely heavy. Whichever design you choose, safety is of paramount importance. A faulty, uneven or incompatible stand will cause the tank to rupture, leading to possible human injury, the livestock and a great deal of mess!
  The ideal stand would be professionally purpose - built for the aquarium and should accommodate all the necessary equipment.