Goldfish Care

Hundreds of thousands of goldfish die annually because of improper care, as most of them are bought by careless parents for their children. By learning the basics of properly setting up a tank and maintaining it, you can ensure your pet goldfish thrives for many years.
 The Aquarium

Setting up the best tank possible for your pet goldfish is the number one step. The biggest reason of goldfish death is also the most important rule: Tank size. Goldfish get gigantic, with most of them easily reaching 8 inches and many exceeding 10. Additionally, they do not have a stomach; their digestive system is just a big long tube. Goldfish excrete more waste faster than the average fish. For these reasons, the best rule is to have roughly 20 gallons for the first fish, and 15-20 gallons per goldfish total in the tank. So think how many goldfish you would like to have to know how big of a tank you will need.

1 goldfish = 20 gallons.

2 goldfish = 30+ gallons

3 goldfish = 45+ gallons

It is recommended that you do not get deep tanks. Fancy goldfish are not good swimmers. They were genetically modified to be shorter in length so the organs are more compressed. While this creates the fattened, signature look of the fancy goldfish, it also leaves them prone to swim bladder problems. This can make the fish float upside down or have trouble swimming. They also have two long flowing tails, making it even more difficult to swim. Tanks that are longer and wider, rather than tall, reduce the vertical pressure that can damage a fancy goldfish’s swim bladder.

The purpose of filtration in a tank is to remove toxic chemicals from decaying matter and fish waste from the water. This is done by taking advantage of the Nitrogen Cycle. When fish poop and organic material is broken down by bacteria in the water, ammonia is released and begins to build up. Ammonia above 0.5 parts per million (ppm) is toxic to fish. In the Nitrogen cycle, aerobic bacteria consume the ammonia and turn it into Nitrite, a slightly less toxic chemical. Another kind of beneficial bacteria converts the Nitrite into Nitrate, which is only toxic at high levels: around 40 or more parts per million. A filter acts as a home for these kinds of bacteria, providing surface area that allows the bacteria maximum contact with the aquarium water and the chemicals inside it.

Since goldfish don’t have stomachs, they excrete waste often. It is recommended that your filter is able to cycle your entire tank ten times in one hour. Filter flow is often measured in gallons per hour (gph) or liters per hour (lph), so you want your turnover to be ten times your tank volume.

20 gallon tank = 200 gph filter.

80 liter tank = 800 lph filter.

Note: Ignore ratings such as “For up to 50 gallons.” These are usually false advertising by the manufacturer, or made to fit tropical freshwater fish, and not goldfish.

HOB (hang-on-back) filters and canister filters are recommended, as these are stronger and more reliable than undergravel or internal filters (which also take up valuable space). I prefer the Aqueon Quietflow series, or the Aquaclear (although it is a bit  more expensive than Aqueon). These contain high quality biological media (the media inside a filter that creates high surface area for bacteria to thrive on) like ceramic rings or bioholsters.

Filters can also physically separate waste, plant matter, old food, etc., from the water using a mechanical filtration media, which is typically a sponge or a floss cartridge. Many brands of filters will say their cartridges need to be changed out monthly, but this is not true. All that does is remove all the beneficial bacteria you’ve built up on the media. Once every month or two you may lightly rinse your cartridge in a bucket of tank water to clean it as necessary.

A third type of filtration is called chemical filtration. The media, usually a bag of activated carbon, binds chemically with pollutants in the water, removing them permanently. This type is not mandatory in goldfish tanks.

Important! Whatever kind of filter you end up getting, be sure to consider fish safety. Make sure your filter intake tube is covered (and that it fits into your aquarium). Fish sucked into a filter can be hurt or even killed.
Decorating Your Tank

When choosing decorations for your tank, remember that goldfish grow very large. In order to maintain appropriate swimming space, the total volume of all the decorations should be no more than approximately a fourth of the tank’s size. Inspect decor carefully for sharp or pointy edges. Goldfish are always on the look out for food, and can carelessly scrape themselves on anything sharp. Also try to avoid hollow decorations with holes close to the size of the goldfish’s head; in their search for food, goldfish can wedge themselves almost anywhere.

The substrate is much more important than most people think it is. Never use gravel. Goldfish can accidentally swallow it when foraging for food, which can be fatal. It also allows a tremendous amount of waste to get lodged between the grains, producing more and more ammonia every day. Goldfish thrive best in tanks with either sand or no substrate at all. Sand is a little more difficult to keep clean than a bare-bottom tank, but goldfish enjoy digging around in it, and black sand can hide waste or uneaten food, so you don’t have to look at fish poop every time you see your aquarium. I prefer to use black sand for this reason, and to keep my fish from getting bored (yes, believe it or not, fish get bored!).
Choosing Your Fish Friend(s)!

There are many varieties of goldfish, such as commons, comets, shubunkins, fantails, ryukins, veiltails, pom poms, orandas, black moors, telescope-eyes, bubble-eyes, and many more. Although all goldfish varieties are the same species, the physical differences between the breeds create limitations in which kind can be housed together.

  • Single tailed, slim-bodied goldfish such as commons, comets, and shubunkin can be housed together.

  • Fantails can be kept with veiltails, ryukins, most orandas, and other hardy fancies.

  • Breeds with extreme body shapes, such as ping pong pearlscales, and breeds with poor or obstructed vision, such as fish with wens, bubbles, and or uniquely-shaped eyes, can be kept together.

Note: Fancy goldfish with poor vision are also more sensitive to water quality and illness, so consider carefully.

Next, considering non-goldfish tank mates for goldfish? Most other fish will bully the goldfish, be bullied by the goldfish, require different water parameters such as temperature or pH, or the goldfish will steal all their food. In general, only freshwater snails, white cloud mountain minnows, and bristle/bushy nose plecos can be safely kept with goldfish. Bushy nose plecos do not get as large as other plecos (which can grow up to two feet long) and are not aggressive towards goldfish like other kinds of plecos are.

Finally, when choosing a goldfish, choose one with a great personality that swims up to you, swims all around the tank, and is not lethargic or bottom sitting. Make sure there are no suspicious spots or blotches on him, or on any other fish in that same tank. Ask a pet store employee to put a small amount of food in the tank. If it takes more than five seconds to swim up and get it, it means he is not very healthy. After you’ve made your decision, select tank mates that are more or less the same type (for example, if you find a really nice telescope-eye goldfish, make sure his companions are either celestial-eyes, other telescopes, or black moors).



It is critically important that the staple goldfish food has 5 basic standards:

  1. The food was designed for goldfish or similar omnivorous fish.

  2. It is in pellet or gel form (not flakes).

  3. It is sinking. Floating pellets require the fish to gulp at the surface, which can damage the swim bladder.

  4. Doesn’t contain ‘meals’ on the ingredients, such as corn meal.

  5. Contains a lot of whole fish or shrimp.

I recommend the brands Omega One Goldfish sinking pellets, New Life Spectrum sinking pellets, and NLS Thera A. Twice a day, feed your goldfish a small pinch of food. Fish under 2 inches should receive no more than 5 pellets total in a day. Fish between 2 and 5 inches should receive 10 pellets, and larger fish should be given 15 total.

To be healthy, goldfish need a variety of nutrients in their food, such as fresh vegetables, just as humans do. In addition to a pellet staple, it is recommended that at least twice a week you feed some type of boiled veggies, like carrots, squash, cucumber, and leafy greens, especially spinach. Once a week you may feed your fish frozen peas that have been boiled for around a minute with the shells taken off. When you shell the peas, the peas automatically separate in two pieces. Feed only half a piece to fish under two inches, a whole pea to fish between 2 and 5, and two peas to fish bigger than 5 pieces total for that day.

An alternative is feeding gel food, particularly Repashy Soilent Green. This is super easy to make and has all the nutrients needed for the fish. You can also supplement (sparingly) with other protein foods, such as live or frozen bloodworms, daphnia, brine shrimp, or tubifex worms. Feed these very sparingly, at most once a week, best every two weeks. Some people buy small amounts of brine shrimp and give them to their fish on their birthday, or other celebrations.


Regular maintenance is a huge part of every pet. Whether it is feeding the fish, testing their water parameters, or changing their water, it provides an interaction between the owner and fish, and after it is finished, the pet is happier. The four kinds of regular maintenance for fish are daily, every five days, weekly, and monthly.


Daily maintenance is an overview of the entire tank.

Make sure the filter is working properly.

The airstone/bubbler is functioning.

  • Make sure the filter is working properly.

  • The airstone/bubbler is functioning.

  • Check that the temperature is between 65 and 75 degrees Fahrenheit.

  • Inspect the fish for signs of disease or stress (clamped fins, bottom-sitting, lowered dorsal (upper) fin, spots or blotches).

  • Twice a day, feed your goldfish a small pinch of food. Fish under 2 inches should receive no more than 5 pellets total in a day. Fish between 2 and 5 inches should receive 10 pellets, and larger fish should be given 15 total.

5 Day

As stated previously about the nitrogen cycle, ammonia, nitrites, and nitrates all need to be kept under control. To do this, check your water parameters for ammonia, nitrites, nitrates, pH and high range pH with the API Freshwater test kit. Other liquid drop test kits will work, but avoid test strips, as they are very unreliable and read wrong results.

Every five days, check to make sure ammonia and nitrite are at 0, and nitrate is at 20 ppm maximum. pH should be between 7-8. Exact pH value doesn’t matter as long as it stays stable over time. Of course, a cycled tank containing enough beneficial bacteria will make short work of ammonia and nitrite, but nitrate cannot be further broken down.This is why it’s necessary to make weekly water changes.


Your weekly maintenance is water changes. Whenever a week has passed since your last water change, or ammonia/nitrite/nitrate are too high, you will need to perform a partial water change. This can be done using a gravel vacuum and a bucket, or a water changing system that hooks directly to your faucet. In these systems, water is sucked up and drained directly into your sink, and then clean tap water is pumped back in. Aqueon and Python are two brands that sell water changing systems.


  1. To begin your water change, turn off your filter.

  2. Activate the siphon mechanism of your gravel vacuum or water changer, and remove 50% of the water from the aquarium. While it is sucking out water, move the vacuum around to suck up uneaten food, fish poop, or other debris.

    • Tip: If you are using a bucket to empty your tank, consider dumping the water into your yard. The high nitrate load is great fertilizer for plants.

Important! If your gravel vacuum doesn’t have a protective screen, keep it away from your fish. Consider covering the end of the vacuum with a piece of netting or sock, secured with a rubber band. Fish sucked into gravel vacuums can be badly injured or killed.

  1. Shut off the water changer or remove the gravel vacuum from the aquarium to break the siphon.

  2. Next, add water conditioner to the tank (I recommend Seachem Prime or Aqueon Dechlorinator).This makes the water safe from chlorine, chloramines, heavy metals, and, in the case of Seachem Prime, Ammonia.

  3. Fill the aquarium with fresh water.

    • If using a water changer, simply switch the device to the other setting and turn on the faucet. Do this first with the valve open so water runs into the sink. This will clear any settled bubbles or dissolved metals from the pipes so they are not added to the aquarium. Then close the valve and water should flow through the hose to your tank.

    • If using a bucket and gravel vac, fill the bucket from a faucet and pour it into the tank. Since this is such a pain and hustle, it ultimately makes the owner avoid doing water changes, so I highly recommend a water changer.

After you have finished up, don’t forget to turn your filter back on and add any plant fertilizer you may have.


Monthly maintenance consists of mostly equipment care. This may include

  • Swishing your filter media in a bucket of dechlorinated water to remove extra gunk
  • Changing out expired chemical media (carbon loses effect after one month, other types may last longer or shorter depending on the type and brand)
  • Scrubbing algae
  • Deep clean of substrate
  • A larger 70-90% water change to make sure all accumulated toxins are removed
  • Rearranging decor (goldfish are very intelligent and will appreciate some new scenery once in a while!)

Treating and preventing infections

If you feed your goldfish properly, give them adequate tank space and filtration, and check your parameters regularly to keep nitrates under control, you might not need to worry about diseases, except for those carried in with an infected fish from pet store. However, it is good to keep a medical cabinet handy, just in case. Even in a perfect tank your fish may get sick at some point in their lives.

  • Aquarium Salt (Pure sodium chloride, with no additives. Do not use table salt!): Reduces stress, helps heal wounds, regrow fins, and battle minor bacterial diseases such as fin rot.

  • Epsom Salt: Draws fluid from the goldfish’s body in the case of dropsy.

  • Spare heater: Raise tank temperature to 80 degrees Fahrenheit to treat ich. Best when used with salt.

  • PraziPro (Praziquantel): Treats and can be used to prevent parasitic flukes. Does not harm beneficial bacteria.

  • Methylene Blue: Fights fungus.

  • Seachem Metroplex: Useful for adding to food to treat internal parasites or bacterial infections. Check out our article on how to use metronidazole

  • API Stress Coat: Helps heal wounds and injured fins, reduces stress.

Next, a brief overview of the most common diseases will help the owner identify if their fish has a disease, which disease, and how to treat it.

Important: Please remember that using a medication that your fish doesn’t need, mixing incompatible treatments, or using the wrong medication for the problem can do much more harm than good. If you’re not 100% sure what your fish has please make a diagnosis thread first and we will help you sort out the best choice to get your goldie back to full health.

  • Ich (AKA, the White Spot Disease): Easy to identify, as you will see a lot of small white spots on the fish, like someone sprayed it with salt or sugar. Other symptoms include clamped fins, and the fish flashing, or rubbing itself on decor. To treat, raise the temperature to 80 degrees Fahrenheit, and add a tablespoon of aquarium salt per five gallons of water.

  • Flukes: Common in newly purchased fish. Fin clamping and heavy breathing, as well as bottom sitting, are signs of flukes. Use PraziPro or other Praziquantel medications.

  • Dropsy: Identifiable by the scales of the fish being raised like a pinecone. You will also see swelling on the belly. Give the fish an Epsom salt bath:

    1. Place the fish in a container with about 5 gallons of tank water.

    2. Add 1/8 teaspoons of Epsom salt per 5 gallons.

    3. Allow fish to soak for 30 minutes. Watch closely for signs of distress.

  • Fin Rot: Fins will be fringed with white, and appear jagged, like the fins are rotting away. Add a tablespoon of aquarium salt for every 2 gallons of water. After symptoms improve, do a 75% water change and add a tablespoon of aquarium salt for every 5 gallons of water.

  • Fungus: White, cotton-like growth. More common on fish with wens, like Orandas, lionheads, and ranchus. To treat, move the affected fish into a different container at least 10 gallons in size, and add methylene blue to the tank. Add a tablespoon of aquarium salt for every 5 gallons of water.

Important! While using any medications, remove the activated carbon from your filter. Activated carbon will remove medication from the water before it can have the desired result.