Grouping.—In Chapters IV. and V. I have enumerated the kinds of animals and plants most suitable for aquaria, and must now caution the beginner against the injudicious grouping together of creatures of dissimilar habits. Anemones may, as a rule, be kept together. The several species agree well, and seldom or rarely injure each other; but star-fishes and crabs are best kept in vessels apart from them. Star-fishes are very destructive, and readily absorb the bodies of mollusks out of their shells. If exception is to be taken to any particular anemone, I think the grand plumosa must suffer by it; for this noble creature gives off a flocculent exudation, which seems injurious to other kinds. I have generally kept the plumose anemone in company with A. mesembryanthemum, A. bellis, troglodytes, and others, without perceiving any bad result; but I have always been careful to remove the slimy exuvia daily, by means of the dipping tube. Respecting mollusks, and especially trochus and most bivalves, it should be borne in mind that they are apt to die off rapidly, and to cause a putrescence of a most obnoxious character, which soon spoils the water, and causes a general havoc. Another remark applicable to mollusks is this, that the Eolids—members of the Nudibranch, or naked mollusks—are destructive of anemones, and delight in nibbling holes in their coats, or eating off their tentacles; whereas the pretty doris may be kept as long as it will live, in company with the most delicate creatures, without offering offence to any. The more varied the collection the more is our interest in its examination increased; and the possessor of a single vessel, or of a tank, and a few auxiliary jars, will be naturally anxious to preserve representatives of as many tribes as possible; and this may be done, to a certain extent, by appropriating the vessels to such creatures as agree amicably in confinement. It is, indeed, possible, if a vigilant watchfulness be observed, to bring together and preserve, for a length of time, specimens of creatures that are naturally antagonistic to each other; but where Crustaceans can be kept apart in one vessel, with perhaps a few fish, such as gobies and blennies—a second appropriated to anemones and madrepores—and a third to mollusks, madrepores, and tubeworms—there will be the greater certainty of success, and less supervision will be required. Crabs are very annoying to anemones, as they scratch and sprawl over the delicate creatures; and shrimps, prawns, and fishes frequently fall a prey to the barbed threads and the tentacles of the anemones; the latter also frequently take possession of the mouths of the cells of tube worms, and of the openings of the shells of mollusks, and thus suffocate the inmates, and insure their own death by the putrescence that ensues upon the demise of their victims.
Sulphuretted hydrogen.—When the death of an animal occurs, the water soon gets putrid; the stones assume a rich brown tint, the sides of the vessel lose their brightness, and an effete odour indicates the cause of the disturbance.
Preservation of the Water.—To those who live near the sea it is an easy matter to change the water, as soon as it shows signs of disorganization, but since the majority of those who will consult this work will have to depend on Mr. Bolton's marine salts, it is necessary that I should suggest in what way, and in the best manner, the water may be preserved, not only to avoid the expense, but the trouble attending a new supply. Charcoal is the grand restorative, purifier, and preserver; and for this department of aquarium management may be regarded as the ne plus ultra.
In the second Chapter of this part of the work I have described the process necessary in preparing artificial water by means of the filter. Now, whatever happens, set the filter to work, it will revive exhausted stock by æration, destroy sulphuretted hydrogen by the contact of the water with the charcoal, and remove all fragments of decayed weed, flocculent threads given off by anemones, and restore the whole to strength and purity. I repeat what I have already said more than once, that the necessity for changing the water is a proof of injudicious management; every new supply is a witness of the aquarian's lack of skill, as Mr. Lloyd wisely says, "properly managed, the water and other contents of an Aquarium may be kept unchanged for periods indefinitely prolonged." For the sake of aquarian science, I do implore the student to surmount any and every difficulty, rather than own the weakness implied by changing the water.
Aeration is frequently referred to in works on the Aquarium. It is at variance with the self-sustaining theory, and there is something wrong where it is wanted. If the tank is stocked before the plants are well established, or if overstocked with a crowd of animal life, or if sulphuretted hydrogen be produced and make its presence manifest to the nose, then æration may be necessary. A cup or jug may be used to dip water from the surface, and pour it back again from a height in a thin stream. Or a filter may be placed over the tank and filled from the surface, and the water allowed to drip back. But the most efficient instrument is a common syringe. This is simply to be charged at the surface, and discharged again with some force, so as to send a stream of oxygenised water deep into the tank. The process should be repeated for a quarter of an hour at least.
Filter.—A bee glass or a common flower-pot may soon be made into a filter. Thrust a piece of sponge into the hole in the bottom, and upon it lay a stratum of washed sand and powdered charcoal. Pass the water through it, and it will be purified, and saturated with oxygen at one and the same time. With the river-tank, the simplest way of reviving exhausted stock is wholly or partially to change the water; with marine stock, such a change is not easy, and the filter comes more legitimately into use. As already remarked, the necessity for æration marks error in management, except when you have stock for which no proper receptacle is at hand, or any such special contingency.
Decay of Plants.—The sea-weeds are apt to acquire a pale tint, which is the first evidence of decay. This generally happens with the first marine stock, when Ulva and Enteromorpha are used to season artificial water. When the water gets ripe, the plants recover and make healthy growth, but if many white fronds appear, lift out the blocks on which the plants are fixed, trim away the decayed portions with a pair of scissors, and then scrub the stones with a small brush in a little waste sea-water, and replace them; they will soon recover. If red plants have been hurriedly introduced, and decay manifests itself, remove them at once, and waste no time in attempts at revival. Mr. Lloyd will supply a new stock for a trifle, and it is better to begin de novo than to attempt to cure the incurable.
Death of Anemones.—If you observe any of the anemones to shrink up like button-covers, lift them out into a shallow vessel, and aerate them liberally. When small beads of gas appear upon them, you may rest assured that they have gone beyond the—
"Bourne from whence no traveller returns;"
for the first outward proof of death is the formation of bubbles of sulphuretted hydrogen upon their bodies, and they should be removed before this spreads and devastates the tank.