Virtually every fish owner has gazed at their aquarium and wondered how many fish can be put there. Unfortunately, aquariums don’t have a stocking chart slapped on the side. As a result, many an owner unwittingly overstock their tank, sometimes with a disastrous outcome. So, how does a fish owner answer how many fish will my aquarium hold? There are several factors to consider, as well as several methods for calculating safe stocking levels.
The real answer is as many as you can be squashed in it! But the real question is: how many fish can my tank hold comfortably? Let’s jump in and discuss further.
How Many Fish Will My Aquarium Hold – The Basics
One Inch Per Gallon Rule
The most widely known rule for stocking a tank is one inch of fish per gallon of water. While this calculation works as a rough estimate, it leaves room for error. Like people, fish are not all the same size and shape.
Stocking a 10-gallon tank with ten inches of slender-shaped zebras is not the same as stocking it with ten inches of full-bodied goldfish. Larger-bodied fish create far more waste and, therefore, require more water volume.
Furthermore, the fish often are not fully grown when first brought home. The adorable little catfish that is scarcely an inch long today could reach a half foot in size when it grows up. The true adult size of the fish must be used in the calculation.
However, many owners have no idea how old their fish is or how large it will grow. Before deciding, always research the fish to determine the adult size.
Another place for error is assuming the tank size is equivalent to the number of gallons of water it holds. A ten-gallon tank filled with gravel, rocks, plants, and a mix of decorations does not hold ten gallons of water. In reality, the water volume is often ten to fifteen percent less than the size of the tank.
So, while the one-inch per gallon rule is a reasonable yardstick, it has flaws.
Surface Area Calculation
The larger the surface area of the water, the greater the oxygen exchange, which in turn supports a larger number of fish. Therefore, the surface area of the water directly impacts how many fish can be kept in an aquarium. A tank that is tall and thin may hold the same number of gallons as a tank that is short and wide, yet they have vastly different surface areas.
The shape difference between the tanks is considered using the surface area rule. The surface area is calculated by multiplying the width by the length of the tank.
Under the water surface area rule, the tank can be stocked with one inch of fish for every twelve square inches of surface area. However, this calculation has many of the same flaws as the one-inch rule. For instance, it assumes a fairly slender fish, which isn’t always the case.
If wide-bodied fish are kept in the tank, the calculation should be changed to one inch of fish for every twenty inches of surface area.
Like the one-inch rule, the surface area rule isn’t perfect. Its primary advantage is that it takes into account unusually shaped aquariums.
Which Calculation to Use?
As a general yardstick for normal situations, the one-inch rule works adequately and is very easy to calculate. If using it, always use net gallons of water, and consider the adult size and the shape of the fish. If the aquarium is a non-standard size, the surface area rule will work better than the one-inch rule. In either case, always do your homework first, and avoid going under the limit rather than over.
Also, do not fully stock the tank all at one time. No more than 25% of the total volume of fish should be introduced at one time. Colonies of beneficial bacteria eliminate toxic fish wastes. Those bacterial colonies need time to adjust to changes in the bio-load.
Introducing fish a few at a time gives the bacterial colonies sufficient time to grow and take care of the toxins produced by the fish waste.
How Many Fish Will My Aquarium Hold – Wrapping Up
We hope that this has been helpful, and as you have seen, the answers to how many fish per gallon questions is not a hard line.
Always keep in mind and remember to give enough space for filtration, chemical levels, vegetation, tank decor, and tank capacity before introducing the first fish to an aquarium.