Aquarium Water Chemistry for Goldfish

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If you survey a group of aquarists, certainly a large portion will testify that their introduction to our hobby was through the amazing goldfish (Carassius auratus auratus). It is not unusual to find hobbyists who have gone 'full circle' by starting with goldfish, transitioning to all aspects of the hobby, and later in life, returning to these magnificent members of the carp family. In many ways, the goldfish is the perfect aquatic pet. They are easy to breed, nonaggressive schooling fish that become quite friendly with their human care givers. With proper care and excellent water chemistry, goldfish can live for decades.

Goldfish

Goldfish in Ponds

Feeding Koi and Goldfish

Maintaining good water chemistry for goldfish is challenging given their constant grazing and reportedly, less efficient digestive system than many tropical fishes. It is a fact, goldfish are messy eaters; the result being a higher demand on the aquarium or pond's filtration system. In short, goldfish create a higher bioload that directly impacts water quality.

Goldfish might just be the perfect aquatic pet. Photo by Stephen G. Noble

Housing

Excellent water quality begins with proper housing. Unfortunately, with so much excellent care information available, goldfish are still placed in tiny goldfish bowls. It is unconscionable for pet stores to sell those inhumane containers for goldfish. Ideally, goldfish should be provided with a large tank or pond. It is not unusual for common goldfish to grow to more than a foot in length. Larger goldfish should be housed in at least 20 or more gallons per fish.

A glass bowl specifically marketed for goldfish. This container is unsuitable for any size goldfish. Photo by Stephen G. Noble

Personally, I over-winter two large goldfish in a 90-gallon tank and find this is about the right size. A rectangular aquarium, such as a 40-gallon breeder tank, is ideal for a few small goldfish. With its 36 inch length, 18 inch width and shallow 16 inch depth, this tank offers plenty of swimming room and provides great surface area for gas exchange. Outdoors, a properly filtered 300 gallon water garden is sufficient for a pair of large goldfish.

Filtration

Besides being continuous, messy eaters, Goldfish defecate heavily and eliminate harmful substances through their gills. They are very sensitive to their own waste and quickly succumb to the effects of ammonia and nitrite poisoning. Goldfish are also sensitive to high levels of nitrates. Powerful biological filtration, circulation, aeration and frequent partial water exchanges help overcome the deadly effects of toxic substances. I am a huge supporter of sponge filters and have at least one in every aquarium. Few if any similar sized filters can compare to the biological filtration of a properly maintained sponge filter. The ideal filtration system would consist of a sponge filter in addition to a hang-on-the-back (HOB) power or canister filter. The HOB or canister filter provides excellent circulation and plenty of mechanical and biological filtration.

Veiltail goldfish. Photo by Bechstein/Wikipedia

Heating

Goldfish are cold water fish which means they are very happy in an unheated environment. Water temperature ranging from 55° to 80° Fahrenheit is tolerable, but 68° to 72° (F) is optimum especially for fancier goldfish. An aquarium heater is not necessary or advised unless a rapid, extreme drop in temperature is anticipated. Bring pond goldfish indoors at the onset of the fall season or provide the pond with a heater to keep a hole open in the ice for proper gas exchange. The Laguna Power Heat Deicer is excellent for this purpose. Please see my review of this product on FishChannel.

Substrate and Decorations

For some reason, there is a belief that goldfish should be kept in bare bottom, undecorated aquariums. Whether the belief derives from hobbyists cramming a bunch of goldfish in small, inadequately filtered quarters resulting in a mess or from simply observing five hundred feeder goldfish in a bare bottom pet shop tank, bare bottom tanks are definitely not recommended. A properly maintained substrate greatly enhances their well being and water quality.

Many hobbyists begin with feeder goldfish. Note the lack of substrate and decorations. Photo by Stephen G. Noble

Substrate harbors huge quantities of beneficial bacteria that convert fish excretions to less toxic chemicals. Substrate also provides the goldfish a place to conduct their incessant pecking in search of food. They can actually be observed playing with the substrate. Goldfish love to swim around logs and large rocks. Such decorations not only make the tank more realistic but no doubt, contribute to their quality of life.

Plants

Given their nature for 'poking around,' goldfish have a much deserved reputation for uprooting and eating plants. But keeping aquatic plants with goldfish is possible with prior planning. In fact, live plants can greatly enhance water quality by reducing nitrates. If the water temperature is maintained within the optimal temperature zone of 68-72° (F), plants such as Anubias, Microsorum pteropus (Java fern) and Taxiphyllum barbieri (Java moss) are an excellent choice. These plants can be attached to logs or rocks helping to secure them in place when pecked by goldfish.

Microsorum pteropus attached to a log or secured to needlepoint mesh is an excellent plant for goldfish. Photo by Stephen G. Noble

Ceratophyllum (Hornwort) and Egeria (Anacharis) are good choices because they can be weighted down or simply left floating and goldfish tend to ignore them. The floating Lemna minor (Duckweed) is an excellent plant due to its fast growth and nutritional benefits for goldfish. They simply devour duckweed. Another floating plant, Salvinia auriculata, does not seem to be eaten by goldfish but they sure enjoy pecking in and around the plant searching for tidbits of food.

Salvinia is an easy to grow floating plant that goldfish generally do not eat. Photo by Stephen G. Noble

Goldfish can easily live in water with a pH ranging from 6.0 to 8.0 with a hardness of dH 5-19. In other words, unless your water source is extremely outside of those values, don't worry about it. Just use water conditioner to remove chlorine and chloramines. Goldfish are very undemanding, easy to care for fish. They are sure to enjoy a long life if you provide excellent water quality through avoiding overcrowding, proper filtration and the conduct of regular partial water exchanges. Enjoy your fish!

Stephen Noble has more than 35 years of experience propagating aquatic, marsh and terrestrial plants. His many planted tanks range from natural to high-tech aquariums. You can reach him via Twitter @StephenGNoble.