This is more than just the actual size of the aquarium. Obviously, a 180 gallon tank would make a poor desktop aquarium just as a 10 gallon tank would be an inadequate room divider. Measurements aside, it is important to also consider how much weight the floor can support, particularly if you’re considering a large tank on any floor with open space beneath. In the 19th century house I live in, I’m fairly certain that a large tank would go straight through the floor and end up in the basement. Some apartment complexes won’t even allow larger aquariums, especially on upper stories. A gallon of water weighs a little over 8 lbs, so water weight in addition to substrate and ornamentation can spell disaster on a weak floor. Saltwater aquariums are also generally going to be heavier than freshwater aquariums – the salt in the water and live rock used in most tanks increases the weight.
In terms of the supplies for the tank alone, a larger tank will usually cost more than a smaller one. Larger tanks will need more substrate, decorations, lighting, filtration and livestock to get the same look as a smaller tank. For saltwater aquariums, a larger tank is going to require more salt mix than a smaller tank. Cost of the aquarium itself and the equipment can vary. While you can generally expect the cost to go up proportionally with the size of the equipment, there are a lot of high-end, high-tech or just plain fancy nano-aquariums and equipment that are becoming hot items in the trade.
Most new aquarists start out with smaller aquarium because they seem easier. In terms of stability and the chemistry of the aquarium, the opposite is actually true. Larger bodies of water are actually far more stable. Imagine adding a cup of food coloring to a kiddie pool, then adding an identical cup of dye to a fullsize swimming pool. The kiddie pool will obviously be much darker in color and will show evidence of that dye far more than the swimming pool will. If both pools are outside on a hot summer day, the kiddie pool will also likely be much warmer than the larger pool (and will freeze much faster in the winter). Aquariums aren’t too different. With all other relative factors equal, the water chemistry in a small aquarium will fluctuate and be harder to stabilize than in a larger system.
This can be tied in closely with stability. A smaller aquarium can take more cleaning and maintenance to keep it stable, but a 10% water change in a 10-gallon aquarium (1 gallon) versus a 100 gallon aquarium (10 gallons) is obviously going to be very different. That same water change may need to happen more often in the smaller tank to get rid of the waste though, but the water change in the larger tank may be much more work. The filtration used in small and larger aquariums is generally different as well. Most larger filtration systems like wet/dry systems can actually take less maintenance than smaller canister or power filters.
Stocking the Aquarium
What fish or invertebrates or plants do you want in your aquarium? Keep in mind that a smaller tank will limit your choices. Many popular aquarium fish will grow too large and/or aggressive for smaller tanks, while others stay very small and may get lost in big tanks. Fish and inverts may have food requirements that can’t be filled if an aquarium that is too small or too large. Some have territory requirements that can cause problems in smaller tanks. Some animlas may be sensitive to changes in water chemistry in the aquarium, while some may require changes in chemistry or temperature to trigger breeding, if you are trying to breed them (see the tie-in there?). This is one of those age-old, chicken-or-the-egg questions – do you buy the aquarium for the livestock you want to put in it, or do you buy livestock for the aquarium that you bought?
These are just a few of the main factors that may effect an aquarist’s aquarium choices. While your own aquarium choice may force you to sacrifice ease for one of the other factors, its important to be aware of each factor before you buy a tank.