This section is from the book "The Goldfish And Its Systematic Culture With A View To Profit", by Hugo Mulertt. Also available from Amazon: The goldfish and its systematic culture.
It being the intention to raise goldfish for aquarium purposes, this final end must never be lost sight of, for with that end in view we direct all our efforts to make the net result in every way satisfactory. To that effect the water in which they are grown should have no current, neither must there be a continuous supply of fresh water from the outside. The natural habitation of the goldfish is standing water, and if they are cultivated in like conditions, they will the better be fitted for the life of confinement in the aquarium.
It is only necessary to add water to the ponds now and then, just as the fluctuations of the season may dictate, and only in quantities sufficient to preserve a uniform height in the ponds. When additional water is required, it should be turned on from the supply drain, in the day time only, as one can then watch it better and keep out any extraneous matter that may happen to be in the drain.
Under no circumstances should it be allowed to run in during the night, nor in the absence of a reliable person who could turn it off in time, in case a storm should come up. Any possible damage to the ponds can be prevented by keeping out the accumulated water during a heavy fall of rain.
The supply drain should always be kept free from obstructions of any kind, and especially when a storm is approaching, it ought to be examined to see that it will quickly carry off the rainwater without interruption.
The grass and weeds that grow along the edges of the dams are to be kept closely cut, for, if permitted to remain, they not only detract from the appearance of the establishment, but they afford excellent shelter for the numerous enemies that constantly threaten the fish. The ponds themselves require a daily examination, and anything found in them that is not wanted can be removed. Bits of cut glass or leaves from neighboring trees do not harm anything particularly, but they are liable to clog the outlet and cause the water (should a storm of rain arise) to rise to an undue height.
Besides these, there will often be found insects, larvae, etc., which can be removed with a dip net, while other and larger enemies may appear that will require the services of a trap or the exterminating influence of fire-arms.
When the fish have been taken out of the ponds in the fall (which is done by draining off the water, to be described elsewhere), the soft mud is removed from them with a hoe. This mud, when frozen thoroughly, will make a first-class compost for flower beds in the following spring. The wire guards from the inlets and outlets, together with the adjustable sections from the drain pipe, are taken into the house for safe keeping during the winter, the ponds being left in a dry state until again needed the succeeding spring. The frosts of winter will kill any remaining vermin, purify and fertilize the soil of the bottom while the absence of water will offer no inducement to muskrats, whose advent would greatly damage the dams.
Any projected changes, alterations, improvements, or the construction of new ponds should be completed in the fall, so that everything will be in readiness for the spring; then a late season that crowds spring-work in the fields and garden will be of little consequence, as the culturist is prepared to take advantage of the first coming of warmer weather.