Periodical Cleansing.—When a tank has stood twelve-months or more, the water not having been changed at all during the whole time, it may be necessary to turn out the contents and re-stock it. This is not to be done unless the bottom has become black, and the roots of the plants show signs of decay, in fact, not unless it really wants it, and if bottomed with mould it certainly will, and it must be done accordingly. The live stock should be removed by means of a hand-net, the water drawn off by means of a syphon of glass, or gutta percha, and the plants taken out carefully and put by themselves, and then after removing the bottom the glass can be quickly cleaned with the aid of water and fine sand, or rotten-stone.
Exhaustion of Oxygen is made manifest by the fishes coming to the surface to gulp air, and it is also manifested by their retiring to the bottom, and quietly extending themselves on their backs in "horizontal repose"—the repose of death. If too many animals be crowded into the vessel, this will soon happen, and either the number must be reduced or the water must be frequently changed, or we must have recourse to æration. I consider the two latter remedies a proof of the incompetency of the aquarian—the necessity marks very bad management indeed.
Temperature.—If the aquarium be too much exposed to the heat of the sun in summer, or to the heat of a fierce fire in winter, the water will get tepid, and signals of distress will be shown by the protrusion of many panting mouths at the surface. I find that if the temperature rises above sixty degrees, things do not go on so well. The use of a blind or paper screen is, therefore, essential in summer time.
On winter evenings, when the room is made cozy by blazing blocks of coal, the collection will often show signs of distress. By opening the lower window-sash one or two inches when leaving the room for the night, things may be restored to a normal state in a few hours, and even if the weather is somewhat severe no harm will be done. At the same time intense cold checks the growth of the plants, and throws the fishes into a state of torpor, and the freezing of the water may cause the bursting of the tank.
In summer time, if the tank should get accidentally heated, it may be quickly cooled by wrapping around it a coarse cloth saturated in water, and keeping it wet from time to time. These matters may be much simplified by fixing a small thermometer within the tank below the level of the water.
Dead specimens must be removed as quickly as possible. Bivalves are generally very hardy, but if death happens to one, the production of sulphuretted hydrogen is very rapid, and quickly fouls the tank.
Disease of Fishes.—I have tried numerous remedies for the diseases which beset fishes in winter, but with very little success. When the caudal fin gets coated with a fungoid growth, I have at once cut it off by means of a pair of scissors, and it has usually grown again in a few weeks. I have a couple of minnows now, that were so operated on last winter, they are as hearty as ever, and their tails are quite renewed. Diseased animals should always be removed to a pan of fresh river water, and placed in a quiet cool place, where they will probably recover.
