Goldfish Basics Care Guide

At Cooranbong Aquatics one of our specialises is goldfish, so naturally we get asked a lot of questions about goldfish. Everything from what temperature and what PH, to what size tank and what medications to use to treat different illnesses. I thought I would write this article to give a good overview of my professional recommendations and what has worked for me in my personal experience, not what the internet tells me to believe. 

Their actual scientific name is Carassius Auratus, goldfish are just a line bred version ,most goldfish are pretty hardy as long as they have nice clean water, this mean no ammonia, nitrites and low nitrates below 40ppm. But the rest of the water perimeters can vary quite a bit, the most important part is to keep it stable and not at the extremes.


Tank Size

Tank size is always a hotly debated topic with in the aquarium fish community, especially the goldfish keeping community, but we personally recommend the minimum tank size for fancy goldfish is 80L for the first and 40L for each one after with a minimum tank size of 200L. For single tail varieties such as comets I personally believe that they are more pond fish, but if you want them in a tank they need at least 120L per fish with a minimum of 350L. And yes, I have been asked what size tank is needed for a koi. I would NEVER keep a koi in a tank because they grow massive and such a big beautiful creature needs a nice big pond to swim around.


Water Perimeters

Temperature can be anywhere from about 14c to 30c for fancy goldfish with common single tail types able to handle temps below zero as long as oxygen levels are maintained. On the upper limits the main thing that limits it is the lack of oxygen in the water because the warmer the water the less dissolved oxygen the water can hold.

Neutral PH is best but honestly I have seen them at both extremes of the scale, it’s just what the fish are used to and any changes must be done gradually.



Then we get to food and what they should be fed. My reply is always, as close to what a carp would eat in the wild as possible. In their native habit, carp and bottom feeders sift the substrate and eat anything in it they can find. They are omnivores and eat a variety of different plant matter, algae and insect but also the occasional food. They pretty much eat anything that fits in their mouth. All my goldfish whether they are fish I have for sale or in my personal display tank get a diet of super green or soilent green Repashy and frozen food such as blood worms and brine shrimp. The latter being used for good effect as a laxative and to help prevent blockages which inevitably cause bloat AKA the biggest killer of fancy goldfish in my opinion. If you’re going to feed Pellets to fancy goldfish make sure they are sinking. Fancy goldfish have a common problem of gulping air while they are eating, while this rarely a problem in long body single tail varieties like comets, in short bodied fancy goldfish the air that they gulp struggles to escape and can eventually cause bloat which normally leads to the fish dying.

It is much better to feed goldfish several times a day, small amounts as they have a relatively fast digestive system and feed as much as they eat in a couple of minutes. Oh and don’t feed flakes pellets and gel food are much better for allot of reasons including that they pellet and gel food retains there nutrients for much longer and they won’t gulp air as much as explained above.


Tank Mates

There is a number of fish that can be kept with goldfish, but you need to follow the general rule that if it fits in their mouth they will eat it. Also remember that that 5cm fantail will eventually become a 15cm fantail with a much bigger mouth and appetite if looked after well. I always recommend not keeping goldfish alone as they seem to do much better in group but do not mix single tail goldfish with fancies unless your will to make sure that the fancy gets enough food because the single tail will be much faster and out compete it. A good non goldfish tank mate can be bottom dwelling catfish such as larger Corydoras They need to be large enough not to be eaten buy the goldfish though, just make sure that you have the tank heated for them. Some people also add sucking catfish such as Bristlenose catfish but you need to be careful as there have been reports that some sucking catfish (mostly common and sailfins) sucking onto goldfish trying to eat there slime coat. Another good option is snails such as mystery snails, they not only look cool but will add a different dimension to the. Whatever fish you choose as tank mates do your research and ask for advice if you not sure.



Treatment wise, we are fairly limited in Australia by choice when it comes to highly effective treatments, especially for treating bacterial infections. The single biggest cause of illness in the home aquarium has to be water quality. A stressed fish has exponentially more chances of becoming ill then a healthy happy fish. But when and if the inevitable happens there is are a few treatments I personally use, my main one is Multicure, as it covers a broad range of things. The other main treatment I use is salt. You can use kitchen salt but I prefer to use the same salt you buy to make saltwater water for saltwater fish. Salt can be used to aid in the treatment of many ailments including, bacteria, fungal and parasites. Sometime treating a fish can be as simple as lots of water changes and keeping the water nice and clean. I will go into this topic in much more detail in a later blog posted.


I hope this blog post has helped answer a few questions, but I’m sure it has also made you think of and ask more. I will be doing a lot more blogs in the future and will cover a broad range of topics and fish, not just goldfish. I will also be doing monthly species spotlight. Feel free to email us at with your questions and let us be your local online fish store. Also check out  for more information.

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