The general norm is 20 gallons for the first and 10 for each subsequent tank, however this is mostly for the fancy goldfish. Any single-tailed goldfish, common or comet, need at least 20 liters of water with extremely powerful filtration. They are incredible trash producers and extremely active fish. If you plan to keep more than one comatose goldfish as a decoration, you will need more than one 20-gallon tank.
Even if they don't make it past puberty, 12-15 year old goldfish can be kept in 20-30 gallon tanks with good care. They are still active fish that require plenty of space to swim around in and hide from danger. Don't expect them to live longer than three years though - most people get tired of keeping them forever and then have to put them down.
If you're thinking about getting a goldfish as a pet, remember that they are easy to maintain but difficult to breed. Also, don't buy a goldfish from a pet store - they are usually sold there because they don't survive in natural waters anywhere outside of Asia. Finally, don't feed your goldfish anything besides lettuce and vegetables - these are the only things that are good for them. Otherwise, they may end up with digestive problems or even worse.
Goldfish are very sensitive animals who dislike many chemicals found in normal household products.
A minimum of 30 gallons is required for a pair of elegant goldfish. If you have a 60-gallon tank, you can fit 5 elegant goldfish or 4 single tail goldfish in there. You may put 9 fancy or 8 commons in a 100-gallon tank. These are the approximate sizes of a goldfish's body when it is swimming upright in the water.
Goldfish like an environment with no current and many different types of hiding places where they can escape the heat of the summer sun and the cold of the winter ice. They also like an environment that provides them with some type of structure to climb on for viewing pleasure or to hide in during threats.
During the first week of owning a new goldfish, the aquarium should be covered with an inch layer of sand or gravel to provide a stable base for their swim bladder (which serves as its brain). If the aquarium isn't prepared properly, the goldfish may sink to the bottom of the container and could damage its internal organs. An injured goldfish cannot recover so please make sure that the container used for your aquarium is large enough and has an adequate number of levels/depths for your fish to swim around in.
Goldfish are very peaceful animals that usually don't require a great deal of space. However, they still need to have room to swim around in so don't buy any more fish than you can afford to house comfortably.
Two to three healthy goldfish can live comfortably in a 40-gallon aquarium, but 50 to 60 gallons is recommended for two common goldfish or up to four miniature goldfish. For a community tank, consider an aquarium with 110 to 120 gallons of water; multiple 20-gallon tanks would also be suitable.
Goldfish are very peaceful and easy to care for, but they do require a constant temperature between 75 and 80 degrees F, with no strong currents or large amounts of movement in the water. The pH level should be between 6.0 and 7.5, and the container should be half-filled with gravel or sand. Provide a small piece of wood as a hiding place for your fish to sleep on and a school plant for them to use as a form of education by watching what others fish are doing. Goldfish are excellent survivors and will usually adapt well to living in captivity.
When purchasing goldfish, look for bright colors that will attract light under their skin and allow them to absorb more sunlight to produce more vitamin D. It is recommended that you change the water every other week and add some salt during high-usage times like during school visits and hospital appointments.
Goldfish have been used in scientific studies to test the effects of medications because of their easy management and relatively low cost compared to other laboratory animals.
I prefer to give each goldfish 100 litres (40 gal) of water. This is a basic guideline that I apply mostly to goldfish, which are the most regularly marketed pond fish in Australia. Smaller fish, such as white clouds, guppies, or galaxias, can be housed in higher densities. Assume 4–10 fish per 100 gallons. A 50-gallon tank would hold 5–15 fish.
The number of fish that can be kept in a pond or aquarium depends on several factors, including size, temperature, and food availability. The amount of space available for fishkeeping also plays a role. In general, more fish means more care and bigger ponds require more space than small ones. There's no set limit for the size of a pond or aquarium, but for optimal health most fish should not be kept in waters with temperatures below 18°C (64°F). Some fish species may only live in warmer waters, while others prefer cooler conditions. The amount of food available to your fish affects how many they will eat. If there isn't enough food, then they will either not eat at all or eat too much and become obese. Neither outcome is desirable! Most fish will eat algae if given the chance. Algae grows rapidly in warm waters and provides nutrients that help fish maintain healthy bodies. Avoid adding fertilisers to ponds, as this will cause algal growth that will need to be removed regularly from the water body.
When you add a single-tailed goldfish, you must also raise the size of the fish tank by 10 gallons. So, if you want to keep five ordinary goldfish, you'll need at least a 70-gallon fish tank. If you want to be safe than sorry, though, an aquarium that size should be more than enough to house all five goldfish.
The amount of space you have available in your home will determine what size aquarium you can get. In general, though, you should look for an aquarium that is at least as large as the number of fish you're keeping plus some room for growth. For example, if you were to keep only three-year-old goldfish, you would need an aquarium at least as big as four years worth of food for them every month!
You should also consider how much space you want to spend on your aquarium. Are you planning to put decorations in it? Do you like to show off exotic animals? All of these factors will help you decide what kind of fish you want to keep and how large an aquarium you need.
Finally, remember that you can always add accessories to an existing aquarium. For example, if you want to display aquatic plants in your tank, you can buy simple ones that fit inside the aquarium and use strings or rubber bands to tie them to sticks placed inside the water.