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Goldfish care

Goldfish are a man made fish and through many centuries have been bred to live in captivity in a similar way to what happened with dogs or cats. Artificial selection not only changes characteristics such as body shape and coloration, but also its resistance and tolerance to life in a confined environment. Goldfish (Carassius Auratus), although considered by many to be a cold water fish, is in fact classified as eurythermal and can thrive in different temperatures and different pH values if it is not extreme. The ideal PH in water is around 7.4 (pH measures the acidity of the water). Goldfish are slightly more tolerant than other fish to some variations in its environment and has a captivating personality. Being a sturdy fish makes people think that goldfish is “bulletproof” and can endure anything which is far from the truth.  Goldfish, as with any other fish, needs clean water, good filtration, a proper tank size and dedication in its care. If you’re buying an aquarium as a piece of decoration in your living room and don’t want expend time caring for it, it’s better to get a sculpture instead.


For stocking rate fish per gallon we suggest 20 gallons to keep 4-5 small goldfish but if they are 5-6” or over, 20 gallons is required for the first fish and another 10 gallons per each additional to allow enough space for continued growth. Filtration needs to be sufficient to circulate around 10 times water volume per hour and partial water changes every two weeks of about 30% to add clean water, dilute toxins and replace trace elements. Also, regular water changes will help dilute hormones such as gamma aminobutyric acid and pheromones such as somatostatin that act as growth inhibitors. Goldfish need areas of rest, especially for the longer finned fish so the water/air on the filter return should be a consideration as to how this is distributed back into the aquarium. Learning the basics and treating your fish as a living being instead of a piece of decoration will provide a long and happy life for any fish.


It’s a common saying among fish keepers that “before you start to keep fish you need to learn to keep bacteria”. Any fish through its biological process will produce waste and release toxins such as ammonia into the water. Ammonia accumulates fast and if you cannot get rid of it your fish will die. Luckily, nature provides the answer to this problem in the form of an army of cleaners, and the process for acquiring this army is called nitrogen cycle.

During the cycling, colonies of beneficial bacteria will grow in the filter media and will convert toxic substances like ammonia and nitrite into less dangerous nitrate. Later that nitrate can be diluted during the partial water changes.

Plants also absorb nitrate as well as some anaerobic bacteria, but basically partial water changes will keep your fish happy and the toxin levels in check. Cycling is a natural process that needs to be done before adding any fish; just fill up your tank with water and start it with all equipment working and add a bit of fish food every few days. Fish food will decompose and generate ammonia to feed your growing population of bacteria. The process can take up to 2 months and can be speeded up with biological enhancers available in any aquarium shop. 

To know if the cycling is taking place you need to purchase an aquarium test kit so that you can check the ammonia, nitrites, and nitrate levels. At first ammonia levels will rise and then drop as nitrite starts to take hold. Nitrate won’t appear until your tank has significant levels of nitrite. As the process stabilizes, Nitrate will form and your Nitrite levels will fall. After you have done the cycling start to introduce fish slowly; add the first fish and test the water then a few weeks later add another one and test again. Especially for new tanks, keeping a good eye on your water parameters is essential and remember that before the cycling you don’t have an aquarium; instead you do have a box of water. 


Always use water conditioner when you add new water to your tank.  The water from our tap comes treated with chlorine and chloramines that kills germs and bacteria to make it “safe” for us. As you add tap water without treatment in your tank it is likely that your beneficial bacterial colony will suffer or die. Never clean your filter media with tap water, always use water taken from your own tank when cleaning is needed.




Water changes do impact on goldfish hormones and toxins. It doesn’t matter how good or expensive your filtration is, what it does is to slow down the decline in water quality. Living beings absorb trace elements (i.e. calcium, potassium, iron) within the water as it grows. There are many different supplements to re-supply your water with those elements. If regular water changes are not made some chemical filter media promises to absorb even some hormones. But nothing is as simple as partial water changes. 

Fish naturally release hormones and pheromones in the water, and some of these hormones will affect fish chemistry or behaviour. Imagine a lake with some fish. They all live well, have plenty of food, space and many of the hormones they release are diluted in a large body of water. As time goes by, the lake comes to a very dry season, the water volume now is reduced and substances previously diluted start to accumulate. The growing levels of hormones such as gamma aminobitirico acid will signal to the fish that it needs to stop growing to better its chances of survival in this situation with scarcity of resources and space.

For a fish in a fresh water tank without water change it's always in dry season due to the small volume of water. Also, some pheromones like somatostatins are produced by fish to suppress the growth of other fish to avoid future competition. The bigger and dominant always want to be the bigger and dominant. Partial water changes help dilute toxins and hormones and provides fish with a healthy environment to live and grow. 


Strong water flow inside the tank isn't good for goldfish, especially for fancy varieties such as the Veiltail.  Provide an area of rest by giving places within the tank with low water current. Most goldfish varieties after centuries of artificial selection are very different from its wild ancestral carp. Double tails, rounded body, telescope eyes and in some cases even the absence of a dorsal fin changes the goldfish hydrodynamics.  Strong currents inside the tank can make fish tired, stressed and consequently sick. In comparing goldfish with a pet dog such as a poodle or pug, these dogs are probably not capable of enduring conditions that a wolf can easily do, but a wolf maybe not the best company as a pet!


Lifespan of goldfish depends on care, genetics and tank environment. The oldest goldfish in captivity recognized by the Guinness Book was about 43 years old when it died. Taking away extreme examples means that if proper care is given goldfish can live up to 15 years. As goldfish are originally from Asia which has a temperate climate, changes in temperature through the year makes the biology of the goldfish very attached to temperature changes. At spring the breeding season starts. During the summer its metabolic rate is high and they eat and grow. During the autumn the metabolic rate starts to slow down and during the winter goldfish can almost hibernate. These slow changes in environmental conditions and metabolic rate also make goldfish live longer. Goldfish raised in tropical conditions with high temperatures such as 26C and over all year will be always on its high metabolic rate and grow faster but will also normally die prematurely. The best temperature to keep goldfish is ambient room temperature as long as there are no severe daily fluctuations, ie the aquarium is not by a radiator which is on during the day and goes off at night. Preferably do not keep goldfish in a tropical fish tank where temperatures are high all year round. 




The best advice about fish disease is to prevent it, and it is mainly done with quarantine. If you already have an established aquarium with fish healthily swimming around it doesn’t matter from where your new fish come from, quarantine it for about four weeks before adding to your main tank.  Experienced aquarists have at least two tanks; one main and one spare to quarantine or “hospitalise” sick fish. The spare tank can be small - about 10 gallons with a small hang on filter and heater (if is needed). To set up just add already cycled media and water from your main tank. Use the hang on filter and replace the water in the main tank with clean water treated with water conditioner and aim for the same temperature as the main tank. 


In quarantine your fish gets used to your water parameters, with the food you provide and if it shows signs of sickness i.e. white spots, fungal infections, fin rot… you can treat it without affecting your main system. Also, some diseases take days or weeks to show signs. If the fish is in the main tank when you realise the fish is sick probably all your other fish are likely to be also sick as some parasites can spread easy and fast.  After 4 weeks if the fish are healthy and eating well you can safely transfer it to your main tank.


Preferably instead of introducing fish into an established tank use a quarantine one (see above). The best method to introduce new fish is the easiest one and is called Pop and Drop Method. Basically put the plastic bag with your fish floating in your tank but do not open the bag. After 20 -30 minutes when the tank water and the water inside the bag are at about the same temperature open the bag, take the fish out with a net and place it straight inside the tank. Try not to mix the water from the bag with the water in your tank as it can bring some hijackers such as parasites. Also, maybe the levels of nitrate in this water is high due to confined stressed fish in a very small volume of water.


However you keep a dog, cat or a hamster, they all live in an environment like yours. If it’s too hot or too cold you know it will affect your pet because it affects you also. If there’s a strange smell around you can easily smell it and deal with the problem. Fish live in a distinct environment; to keep this environment healthy it is important to establish a routine. Many people start in the hobby excited but as the months go by the tank maybe gets less and less attention and when people realise that something isn’t right with the fish fighting for air or in foul water it is maybe too late for the fish. 
As with any other pet, fish needs care and as previously stated they can live up to 15 years.
How it will get there depends on you.

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