CHAPTER XII.
HINTS ON AQUARIUMS
It is better to have several aquariums than one. Often the mistake is made of gathering together all kinds of savage and voracious creatures that prey upon each other. Pretty as they are, there is no need to buy the glass aquariums, and indeed better in every way for the inhabitants is a large tub put out of doors in a place where there is not too much sun. Clean sand or gravel should be strewed upon the bottom and in this water-plants may be fixed. If you have any bivalves they will love to burrow in it, and some kinds of fish love to rest upon a bottom of this kind. Large stones should be built to reach half-way up the tub, with spaces between so that the fish may dart out of the light whenever they wish. If you keep fish that need running water it will be necessary to put the tub under a tap, and to pierce a hole near the top of the tub for the superfluous water to flow away. In this case it will be as well to cover the tub with a net, or the fish may be found to have leapt over the edge. Boys may make their own net from the instructions given in Chapter XIX., or may buy cheap gauze or other similar material.
If the tub is for newts and such things as do not live wholly in the water, then the stones should be built until they come above the water and so form a little island. For these creatures the water should not be so deep, and there should be an abundance of weeds.
Freshwater shrimps and crayfish should have a shallow tub or trough, a sandy bottom, and places in which they can hide. Here, too, there must be water running in and out always. By these means we imitate the natural surroundings of the shrimps and crayfish, for they delight in the running water of shallow streams that have a bottom of sand and stones. The outlet for the waste water should be protected with a grating and probably with gauze, or some of the inhabitants of the tub will escape.
There are many objections to glass vessels, though some of their faults may be corrected. They trouble the fish with too much light, but if a brown paper case of the same size and shape as the aquarium be made it can be slipped over the vessel and removed occasionally when you wish to observe the movements of the fish. Glass soon becomes foul, and needs frequent cleaning. In any case the aquarium should be kept out of the sun, and for this reason a northern window is best. Whatever form of aquarium is selected there must be soil and sand at the bottom, weeds, and shelter for the fish. The bell glass is the least favourable form of aquarium, but even that may be made tolerable if the hints we have given are adopted. In the square or oblong form only one side need be glass and the remaining three sides wood, metal or slate. The sand that forms the bottom of an aquarium should be quite clean. If you have found it in the bottom of a swift stream it will not need much washing, but if from any other place it should be washed thoroughly. Put a large bucket under a tap, and as the water runs into the bucket strew the sand gradually into the moving water with one hand, and stir the water as hard as you can with the other. Keep this going until the water that runs out of the bucket is quite clean. Even now, however, the sand may not be thoroughly cleansed. Put a drop of the water upon a piece of clean glass, and when the water has been evaporated there should be no sediment. When the sand, plants, pebbles and stones have been arranged in an aquarium it is best to introduce the water gently by means of a syphon, a method explained in Chapter XIX. The aquarium may be emptied in the same way.
There are a number of ways of supplying the fish with the amount of oxygen they need. One is to change the water frequently, another already mentioned is to have running water and a pipe for the surplus water; a third means is to have a fountain, an attractive element described in Chapter XIX.
These methods, however, are mechanical and artificial. The natural way of providing the oxygen is to secure the aid of water plants. These absorb carbonic acid gas, and, having made use of the carbon in their growth, set free the oxygen, which is waste as far as they are concerned. Thus in a well-balanced aquarium the fish provide the plants with carbonic acid gas, and receive back the oxygen which they need; the plants provide the fish with oxygen which they do not want, but which is the very life of the fish, and receive back the carbon without which they would die. Water-beetles, newts and some other creatures come to the surface for their air, and take no oxygen, or very little, from the water.