Scavengers are the Sanitation Department of pool and aquarium. They keep them tidy and the water sweet by consuming excess algae as it forms on plants and on the sides of pool or aquarium, and by consuming fish offal, scraps of food, or even dead fish that sink to the bottom unobserved.

   The term scavenger is practically synonymous with snail, for snails do the bulk of the work. There are other scavengers which do fairly well, but they are insufficient without snails.

   Snails also serve as a living meter which indicates any drastic chemical changes taking place in pool or aquarium. A slightly acid condition of water, healthy for goldfish, causes the shell of a snail to become pitted and scored. That will be your indication of a healthy pool. Extremely acid water, dangerous to fish, will first kill snails.

   If snails cling to the surface rim of pool or aquarium for as long as a day, the water may be out of balance. If you investigate and find the water foul, change it. If the water is not cloudy and has no odor, assume that the snails are objecting to acidity or to an exceptionally high oxygen content. Neither of these developments is dangerous to fish.

   Even though snail breeding is a quick and simple procedure, few find it worth doing since snails seldom need replacement and are quite inexpensive. If you want to breed a few, however, set aside an aquarium or bowl which has been used long enough to acquire a pretty good growth of algae. If you must use a new container, transfer to it some of the water and algae from pool or aquarium.

   Snails deposit eggs on plants and on the walls in gelatinous masses about as large as a thumbnail. Start a brood by plucking the eggbearing plants and dropping them into the container you have prepared or by transferring a few adult snails. Eggs left where fish can get them will usually be eaten. If the fish do not get the eggs, then they will eat the young snails of most species as soon as they appear.

   Eggs hatch in three weeks. Sprinkle flour or pulverized fish food into the brood container, and remove the adults at that time so they won't eat all the food. When the young snails are large enough to move around (after a week or two), feed them lettuce, cabbage, melon rinds, tomato peelings, bananas, cooked spinach, or practically any other fruit or vegetable scraps you have.