About Coldwater Fish

It is a frequent scenario that a newcomer to the aquarium hobby has a belief that before launching into acquiring a tropical freshwater aquarium, experience should be gained by keeping the “easier” option of a coldwater aquarium. The concept is usually one of an aquarium with common goldfish, or goldfish fancy varieties. In many ways this belief is seriously flawed, as many of the tropicals are very much easier to keep, and permit the aquarium to be kept presentable with far less of the hands-on attention usually required by a goldfish aquarium.

However, with this premise understood, the coldwater aquarium can be a delight to have. In these days of many homes being centrally heated, the coldwater aquarium is, in fact, rarely what could be described as truly “cold”. Normal room temperature for the unheated aquarium, however, is perfectly acceptable by the majority of what are termed “aquarium coldwater fish” and “tropical aquatic plants”. However, to avoid stressful variations in temperature it is recommended that a heater should be installed in the coldwater aquarium wherever practical. A steady temperature will be maintained to the overall benefit of the fish and plants.

In spite of the firm’s name, we at The Goldfish Bowl do not recommend the bowls available on the market today for ideal fishkeeping. We do sell them, and carry a very comprehensive selection of types and sizes, but we prefer to guide prospective customers towards the more fish-friendly aquariums – also stocked in a big variety of types and sizes.

Most of the coldwater fish stocked for the aquarium hobby are goldfish, or some of the many varieties that have evolved over many years of selective breeding into what is generally termed “fancy goldfish”. Although most often seen as yearlings, or younger, these fish are purchased as babies, which have the potential to grow into large fish. This should be considered when planning what size aquarium to buy, and realising that the initial stock will soon begin to grow to take up the available space. The mistaken idea that the fish will only grow as big as the aquarium dimensions will allow can result in a grossly over-stocked goldfish aquarium. Some fish may stunt their growth due to space restriction, leading to an unhealthy animal, while others eventually may die from stress simply because the space has become too cramped for them. Either stock what you can properly accommodate, or be prepared to progressively part with some of the stock to a garden pond keeper, if that accommodation would be appropriate to the species or variety you need dispose of.

Goldfish Aquascape

Goldfish Aquascape with Red and Silver fan tail and Red Lion Head Goldfish in a planted aquascape setting.

Coldwater Aquascape

Coldwater Aquascape (temperate aquarium) with natural plants, sandstone and burnished goldfish.












Goldfish and many other coldwater “coarse” fish, such as rudd, etc., eat ravenously, and excrete copiously, so the filtration system you choose should be entirely adequate to cope with this factor. Using a filter which is apparently oversized makes sense in this situation. If you can accommodate an outside fitting canister filter this will undoubtedly be the best system to use, but with more regular maintenance an inside fitting power filter can suffice.

Lighting should be carefully balanced to avoid algae growth, as control of this menace by including an algae eating fish is not so easily achieved in the coldwater aquarium as it can be in a tropical set-up. As with any aquarium it should not be routinely exposed to direct sunlight or even strong daylight, and if the positioning of the aquarium must be in such a situation, a means of shielding it from the excess light should be considered at times when the aquarium is not needed to be exposed for viewing, such as when the occupants of the house have left to work, for example. If natural plants are to be grown in the coldwater aquarium select those with tough leaves, as goldfish will often strip the more delicately fronded plants of their leaves in no time. Species of Anubias are quite good for this purpose, also Java fern, having thick leaves resistant to being munched away, and being very tolerant of low light levels when required. Egeria densa is often known as “goldfish weed” and is very popular for coldwater aquariums, due to its fast growth rate and general hardiness. However, the fish will usually feed from this plant too, as it lacks the sturdiness of the previously mentioned species.

Feeding goldfish is rarely difficult, and most will quickly become tame enough to take food readily from the owner’s fingers. Over-feeding is the single most common cause of disaster in any aquarium, and perhaps particularly so in the coldwater aquarium. The usual strictures about minimising the amount of food per feed during the initial period, when the new aquarium is maturing its filter medium, can lead to misunderstanding and a continued regime of virtual starvation. The amount of food should be little, but the regularity of the feeding should be often. At least twice a day, and better still three times a day, is the best approach. And remember that the stingy amounts being offered in that crucial filter maturing period are not sufficient for the ongoing, long-term, welfare of the fish, and must be increased to a proper and adequate amount once it is safe to do so. The Goldfish Bowl offers calling customers a free water testing and monitoring service to help you through that initial period, and by taking advantage of that you are able to assess more reliably when and how you may safely progress to correct regular feeding.

One of the commonest complaints the fancy goldfish can develop is that of swim bladder derangement, when the swim bladder retains too much internal gas and results in the fish being unable to leave the water’s surface. Occasionally but less frequently the opposite occurs, and the fish is unable to get off the bottom without a good deal of energy-sapping struggling. The round-bodied fish are particularly prone to this condition, due to the congestion of their internal organs within the globular body profile. Good feeding is often the means of preventing this distressing complaint. The fact that it is possible to maintain a goldfish throughout its natural life with nothing more than one kind of dried food is its downfall. The dried food is dehydrated to a considerable degree, of course. When digested it will absorb water and swell significantly, pressing against already precariously positioned internal organs, which can in turn cause permanent swim bladder derangement. Soaking the food before feeding it is a partial remedy, but by feeding a much more nutritious diet, including some frozen natural foods of shrimps, insects, and other meaty products, the problem will most often be completely avoided.

Coldwater aquarium

Freshwater, coldwater aquarium with yellow sandstone and natural plants with a selection of fancy goldfish.

Coldwater Aquascape

Coldwater Aquascape (temperate aquarium) sandstone with natural plants and red and white goldfish.












Part water changes are essential to the maintenance of good water chemistry. If the aquarium needs topping up due evaporation and a fall in the water level, a part water change should be carried out at the same time. This will ensure that a dangerous build-up of residual elements left in the water as only the pure water evaporates, will not continually increase in density to become an unseen hazard for the fish. In addition nitrate build-up will, in most cases, also be regulated in this way. The filter needs far less frequent attention than this water changing discipline, and its filtering medium should only be gently washed free of built-up detritus when necessary. It is better to leave the filter undisturbed as far as is possible, and as long as it is not overloaded with detritus and still pushing the water through at a good flow rate, it is best left to carry on with its essential water chemistry control. NEVER scour the filter medium, thereby removing the miniscule essential nitrifying bacteria it hosts! Wash it gently and with great care. The recommended approach for this is to do the job at the same time the part-water changes are made, so the filter mediums can be rinsed through in the siphoned off aquarium water, thereby minimising undue nitrobacter loss due to change in the water chemistry and /or temperature. When making water changes always use water conditioners to safeguard against the effects of chlorine and other hazards. “Stress Coat”, “Stress-zyme” are recommended products for this purpose. Adding special aquarium salt to the water is also beneficial, and when a proportion of the “dose” is removed by the part-water changing it should be replaced with a comparable amount.

Other species of temperate fish are frequently offered to the fishkeeping hobby, and advice should be sought as to how well they may mix before rushing into buying what makes a pretty collection, only to find there are some among them, which nip and tear fins, or generally harass their tank mates. Even the docile looking goldfish can have a nasty streak, and it is not uncommon where two fish have been bought, for one to become the dominant boss, and worry its companion to an early death. When there is a small group of four or five fish, even if there is a dominant one among them, the selection of potential victims usually results in them all having enough respite from persistent bullying to get along all right. But removal of any aggressive fish is recommended, as few will quieten down from this condition to become sociable.

It is a fascinating fact that when we take a fancy goldfish variety into our care we may be nurturing a strain that has been in the making from selective breeding by ancient Chinese breeders since as long ago as 400 AD. Japanese breeders are accredited with building on this Chinese work since about 1600 AD, bringing new colours, different body shapes, and finnage variations. When we are able to raise some young goldfish from the eggs they so freely release in the season, we first see very plain greenish fish develop, resembling the natural colour of their ancient ancestors. Only a proportion will change into the different colours we enjoy so much, and only very few of the fancy varieties will attain prize-winning perfection.