Legend: According to some sales people at fish stores, and some other folks, a general guideline for stocking a freshwater tropical fish tank is that you should not exceed 1 inch of fish per 1 gallon of water. This means that you can fill a 10 gallon tank with 10 1" fish, or 2 5" fish, and the tank will get dirty at the same rate either way. Most people realize that this is not true - the shape of the fish, as well as its eating habits, metabolism, etc. will change this number quite a bit. It still remains a commonly used guideline though, when trying to convince someone that 5 goldfish shouldn't go into a 1 gallon bowl..:)

The reason I made this chart is to demonstrate that my 55 gallon tank is overcrowded, and for the heck of it. Because most of my fish are fairly small and streamlined, this guideline is somewhat reasonable for me - I think eliminating 10" of fish would be a good thing.. right now, we change 50% of the water once a week, and the pH typically drops from about 7.0 to below 6.4 each week, from fish wastes, etc. It's awful, but ironically, the tank looks quite nice (I think algae refuses to grow under such conditions), and the fish are fairly healthy, so we haven't felt a great need to change things. Gotta get rid of those convicts.... *grin*

Another common guideline emphasizes the available surface area of the water, instead of volume, per unit of fish. Personally, I think the volume of fish is a much better judge of its metabolic needs than its length, and can be easily determined by plopping the fish into a container with a known amount of water (like a big measuring cup), and measuring the amount of water the fish displaces in ml (cubic centimeters). This would be a more accurate way to estimate the amount of water volume and surface area a fish would need in a tank, especially fish that have unusual shapes, like fancy goldfish.

Last Modified June 13, 1997