In all other respects, what has been already said on the subject of vessels must be understood to apply to all kinds of aquaria; the rectangular tank, and the bell glass, are the two leading forms, and to them I shall always refer when speaking of the tank in a general sense.
FITTING UP—MATERIALS FOR THE BOTTOM.
Coarse sea sand and pebbles, all well washed, make the best bottom; but if sea sand is not to be conveniently obtained, common silver or gritty river sand will answer every purpose, if washed until they cease to stain the water. Most writers on aquaria—Mr. Gosse especially—condemn silver sand, but I find it a most suitable material: its appearance is cleanly, and it only requires frequent washing in fresh water to fit it for the purpose. In the water-pipe which runs along the wall to supply the kitchen, I have had a hole pierced to form a jet, and this I find of great service in many aquarian operations, and especially in washing sand and pebbles. Where this can be done conveniently, or where the pan containing the materials to be washed can be placed under a tap turned on so as to drip rapidly, the washing can be accomplished with very little trouble, and the materials can remain for a week or two, being stirred up occasionally to hasten the dissolution of solvent matters. The sand should have a depth of two or three inches on the floor of the vessel, and above it should be placed a layer of pebbles, also well washed. The little white pebbles found among gravel look bright and pretty, and if the aquarian is also a lover of the garden, he will turn up plenty of them in digging, so as to keep a supply at hand for use when wanted. The pebbles are not essential, but the sand is, because many of the creatures delight in burrowing, and must have opportunity afforded them of living their own life in a state of confinement.
Rock work is generally considered an essential of a marine tank, but experience has convinced me that the less we have of it the better. I have, in describing the fresh water tank, given instructions for its formation, and here desire only to caution the beginner to repress, as much as possible, any desire for mimic arches, caves, and grottos. In the first place, it must be remembered, that every cubic foot of rock work displaces a cubic foot of water, and reduces the capabilities of the tank for supporting a number of creatures. The more rock the less water, and the less water the fewer animals. Beside this, it is questionable if the use of cement of any kind is advisable; free lime may be expected to dissolve out of it, however much seasoning it may have previous to the introduction of the stock; and as marine creatures are more delicately constituted than fresh water ones, the subsequent loss of many may fairly be attributed to the presence of cement.
In the place of built-up arches, a few rough pieces of stone tastefully disposed at the bottom may be made to produce a good effect: a rough block of granite, or a stem of branching coral in the centre will be far preferable, except for vessels of large size, in which pyramids and arches may be less objectionable. It must be borne in mind, however, that rock work in some form or other is useful, as affording shelter and shade to such animals as love seclusion, and that, in a well managed tank, the rough blocks often get coated with a vegetable growth that increases the strength of the collection, and adds very much to its beauty. In this matter, the mischief arises out of the desire of beginners to display more ornament than is consistent with the nature of the case.
The water, of course, may be obtained direct from the sea, and should, if possible, be dipped in mid-channel. Shore water is not altogether objectionable, for where we find the greater part of our specimens it is evident the water must be suitable for them. In fact, I have found water that I have brought from the sea-side in jars serve just as well as that supplied by the steamer from the open sea; but near the mouth of a river it would be found unsuitable, as it would, also, from any parts of the coast where land springs abound. Earthenware vessels are the best for the conveyance of sea-water and specimens, but if a large quantity be required, a new cask should be used, and the greatest care taken to have it stopped with a new bung, and conveyed quickly to its destination. Mr. Gosse recommends a cask of fir-wood if it can be procured, "the wood of the oak, of which wine casks are usually made, gives out tannin or gallic acid to the contained water, which by its astringency, converts the animal integuments into leather." In fact, our poor anemones get their hides tanned if any vegetable bitter comes into contact with the water in which they are to be kept. I make it a rule to filter sea water through charcoal before using it; this is not essential if the water appears bright, but is, at least, a precautionary process that may have its advantages.
Artificial Water is now used so extensively as to justify some special remarks here upon it. It must be understood that where real sea water can be easily obtained, as at spots near the coast, it is undoubtedly the best, though, in some respects, the artificial preparation is preferable, because less liable to certain eccentric changes of constitution, which will fall under our attention further on. Sea-water contains the spores of plants, and the germs of many forms of animal life which may have development in the tank, and when these births occur, it is a special gratification to the possessor. But such germs may also decay, and cause putrescence; and if a tank is neglected, the water is liable to get cloudy, the stones black, the sides of the vessel semi-opaque, and the animals diseased. Death soon sets his black seal on the undertaking when such a state of things occurs, and the collection, however costly or well formed at first, may be lost. Now such misfortunes as these are preventible, as it will be my duty to show presently, but I here call attention to the fact, that artificial sea-water is much less liable to get out of condition from the very absence of organic matter, which on first reflections, we should regard as a disadvantage. Thus, the prepared material has certain advantages over the natural; we lose the chance of rearing new additions to the stock through the introduction of minute organic germs; but incur no danger of those same germs perishing and polluting the bright lymph.