Buying and maintaining an aquarium can be complex and costly, but a DIY aquarium can be simple with a little planning and attention to a few details. The most important decision is the first one – where to put it. The second and third decisions are almost as important – what shape it will be and how big a tank to use. These need to be settled before construction begins, as tanks are bulky and water is heavy. A 20-gallon tank weighs about 225 pounds after it is filled, and is very hard indeed to move when it is full of water. The tank needs to be big enough for the fish you plan to put in it; most experts recommend a tank holding at least 10 gallons, so that mistakes in the amount of water or the size and number of fish added will not be harmful to fish or plants. It is also important to budget enough money for tank and contents. Most aquarium builders underestimate what they will need, how big and how heavy it will be and how much it will cost.
A tank holding under 10 gallons will be difficult to maintain, as toxins accumulate and temperature and oxygen levels change much faster in small volumes of water. Any aquarium of 15 gallons or more will weigh over 200 pounds when filled, so an adequate and strong surface for it to rest on is necessary. The surface area of the water should be larger rather than smaller, and this means that a shorter aquarium of greater length is better than a taller and thinner tank. It is always safer with a DIY aquarium to have more water and fewer fish; you can always adjust this later once the fish are in place and comfortable.