Information on the Capacity of Common Home and Office Aquaria
(The First Tank Guide)
Many people are curious about the number of fish they can safely keep in their home aquarium or fish bowl. There are many factors that contribute to the population that your aquarium can safely support. These include the type of fish kept, the size of the fish tank (both by volume and dimensions), filtration, and maintenance performed. There are three things to keep in mind when discussing your tank population: tank capacity, fish size, and space required.
Available Aquarium Space
Of all these factors, the first and most important is available space. That means water volume. Before considering any other issues, you need to have sufficient water volume to absorb and dilute the fish's waste before the filter can process it. At the same time, you need enough water volume and sufficient surface area to effectively exchange carbon dioxide and oxygen, and then distribute that oxygen through the water.
Filtration and Tank Population
Filtration is really a secondary issue, but it is very important. Of course, filtration is a nearly a binary consideration at this point: Either the fish tank is sufficiently filtered and the filter is properly maintained, or it is not. If the filter is not sufficient for the tank, or the filter is not properly maintained, the filter is of little or no benefit. Having no filter or a poorly maintained filter, or an insufficient filter greatly reduces the total safe population of the tank, but ironically, over filtering the tank does not increase the holding capacity. To increase the holding capacity of the tank you need to increase the water volume in the tank.
Aquarium Maintenance and Tank Population
Like filtration, the routine maintenance you perform on your fish tank impacts the number of fish you can keep. Unlike filtration, however, you can increase your maintenance - mostly by increasing water changes dramatically - to support more fish in a confined space. You just need to remember that you are having to do a lot of water changes to remove ammonia and other waste from the tank and to allow the water to remain oxygenated. This is really the primary method for making a small fish tank or bowl temporarily viable until you can get a suitable and healthy aquarium for your fish.
Remember, you want to provide enough space for your fish to grow to their healthy, mature, adult size. You need to provide sufficient water volume to dilute the fish's waste until the filter can process that waste. You need to provide the necessary routine maintenance on your fish tank to keep the tank healthy and therefore keep the fish healthy. And you also need to provide appropriate filtration for the tank so that the fish's waste can be processed effectively between water changes.
And always keep in mind that ALL the fish and animals in your fish tank contribute to the aquarium population. That includes catfish, snails, shrimp, sucker mouthed catfish, and other fish and animals in the tank, whether you got them "to do a job" or if they just showed up some how. They all contribute to your aquarium population because they all produce waste in the water and they all consume oxygen from the water.