Covering for the floor of the aquarium is far more important than you might suppose. The ideal covering is sand of medium coarseness, the grade used for making concrete. This remains loose enough at all times for the roots of aquatic plants to spread and draw sustenance from it. Use a l- to 2-inch layer of it.

   Fine sand packs down and becomes too hard for roots to penetrate. Coarse sand is to be avoided if the particles are large enough to hide fish droppings and bits of food. Such tiny scraps, if the snails or fish can't find them, decompose and foul the water. For this same reason, pebbles, small stones, and marbles-regardless of how pretty they look -are to be avoided.

   Now and then the sand will become dark and foul-smelling, for no apparent reason. More often than not, I suspect, this is a result of insufficient sunlight. Aquarium plants which get the required two hours usually do a good job of drawing enough food material from the aquarium floor to keep the sand sweet. Try giving the aquarium a little more sun if this trouble develops. In the meantime, the sand can be sweetened quickly by rinsing to remove all foreign matter, and then spreading it out on a newspaper to dry in the sunshine.

   Dressing up the aquarium with a bit of greenery is the next step, and oxygenating plants for this purpose are discussed in Chapter 12. Some fanciers advise a plant for every square inch of aquarium floor. The plants need not be dispersed over the entire floor, of course, but can be arranged artistically in clumps and borders, much as marginal plants are arranged around an outdoor pool.

   Others maintain that one aquatic plant for every 4 square inches of aquarium floor is enough. In my own aquariums, I plant at a rate about halfway between these two schools of thought, and mine are so balanced that they do not need frequent changes of water.

   Before planting any aquatics in aquarium or pool, trim off all dead leaves and branches and examine each plant carefully for insects or eggs. You can play doubly safe, as I do, by immersing all new plantings of aquatics in disinfectant before introducing them to your pool or aquarium. I use household ammonia and water in a 1 to 50 mixture (4 teaspoons to 1 quart or 1 cup to 3 gallons) and let the plants soak in this for two hours.

   Buy any of the hardy breeds of goldfish at any time of year. Select them for beauty and generally healthy appearance.