Fanciers long ago reduced this business of pool, bowl, and aquarium capacity to formulas, and these are easily applied.

   First figure the area of water surface. Most pools and aquariums are straight-sided and can therefore be filled to any suitable depth. Most bowls taper in at the top, so fill these only to the point of widest dimension, thus providing the greatest possible water surface.

   Figure out the water-surface area in square inches. For square or oblong pools and aquariums, multiply width by length. In round bowls and pools, multiply pi (3.1416 or 22/7ths) by the square of the radius. Simply estimate the surface area of irregular pools (unless you remember a lot more plane geometry than I ever knew) and, to be on the safe side, make your estimate low.

   With the area of the water surface determined, stock the pool or aquarium with no more than 1 inch of fish (not counting the tail) for every 20 square inches of water surface. As an example, a 10- by 12-inch aquarium would present 120 square inches of water surface. That would allow comfortably for 6 inches of fish-one 6-inch fish, six l-inch fish, three 2-inch fish, or any other length combinations you want.

   Fanciers disagree somewhat on the amount of surface to allow for each inch of fish. Some allow 24 square inches, others feel 18 square inches is enough, especially for the rugged common goldfish. In my experience, I have found that a 20 square-inch allowance works out well, and that is the recommendation I make to you.

   Now let us modify this capacity rule in two ways. First, let it apply only to the hardier goldfish-common goldfish, Comets, Japanese Fantails, and other forms rugged enough to spend the winter under ice in an outdoor pool. Allow the more elaborate forms-Veiltails, Moors, and so on-25 square inches of water surface to every inch of fish.

   Then consider that the larger the fish, the more oxygen it requires per inch of length. A 5- or 6-inch goldfish, for example, uses more oxygen than five or six 1-inch fish. This does not amount to a very great increase in oxygen needed, but in an aquarium full of fish it is an appreciable factor. So, once again, play safe by keeping your estimate low and tend to understock rather than overstock. (Heaven only knows how much potential business I am throwing out the window with this advice, but I would rather have a dozen well pleased new customers than twice that many disappointed ones.)