Pet Keen is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Home > Goldfish > Do Goldfish Need a Filter? Our Vet Explains

Do Goldfish Need a Filter? Our Vet Explains

goldfish in freshwater

Vet approved

Dr. Luqman Javed Photo

Written by

Dr. Luqman Javed

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

You may have seen goldfish living in a bowl with no filter, air stone, or aeration. You may have even owned a goldfish that lived this way. Some people have anecdotally claimed that goldfish live for decades in this type of setup, which often leads to discussions not only around the ethics of keeping goldfish in a bowl, but of keeping goldfish in unfiltered environments. This may have left you wondering if goldfish actually need a filter. Here are the facts you need to know about goldfish and filters.


Please Note

In many parts of the world, it may be possible to win a goldfish at a carnival, fair, or festival. We do not recommend or advise adopting a goldfish this way unless you are able to provide a suitable home for them. Legislation in recent years has led to some countries imposing a ban on having goldfish given as prizes at fairs or carnivals.

At Pet Keen, we do not encourage or recommend placing goldfish in bowls as it is very difficult to cater to their needs in such a setup. Goldfish are social, messy, large, and long-lived, and they should be kept in groups in aquariums large enough to house them. Please note that some cities, counties, and jurisdictions have passed legislation that prohibits housing them in bowls.

The Fiction

The belief that goldfish don’t need a filter is incorrect. Goldfish need filtration and can live long lives in the correct setup. Your goldfish absolutely need a filter.

The role of a filter in a goldfish’s tank cannot be understated. Filtration provides your goldfish with several benefits.

All fish filters have two main functions:
  • Mechanical filtration: helps trap and remove debris from the water
  • Biological filtration: helps neutralize ammonia and nitrite, both of which are very toxic for pet fish
In addition to these, some filters also offer the following benefits:
  • Chemical filtration: helps neutralize dangerous chemicals in the water
  • UV filtration: kills harmful pathogens and some strains of algae.
goldfish inside tank
Image By: Hans, Pixabay

divider-fish The Facts

Goldfish not only need filtration, but it’s a really, really good idea to give them high-quality filtration. Goldfish are heavy bioload producers, which means they create a lot of waste. These waste products build up in the water without filtration.

What this means is that you should opt for a filtration system that can go through at least 5 – 7 times the volume of your aquarium every hour. For example, if your goldfish are housed in a 50-gallon aquarium, opt for a filter that is rated for at least 250 gallons. If you cannot find such a filtration system, you can add multiple filters to your aquarium so that they collectively reach this target.

It is not okay to keep a goldfish in an unfiltered tank or bowl and not perform regular water changes. You should be checking your water parameters weekly or more frequently so you know if your tank is retaining ammonia and nitrites, which can be dangerous to your goldfish. If you are checking your parameters multiple times per week, this can help guide you in determining how frequently you should be performing water changes. In a well-stocked aquarium, you should be performing a 25% water change every week.

Understanding the intricacies of water filtration can be tricky, so if you're a new or even experienced goldfish owner who wants a bit more detailed information on it, we recommend that you check out Amazon for the best-selling book, The Truth About Goldfish. 

The Truth About Goldfish New Edition

It covers all you need to know about creating the most ideal tank setup, goldfish care, and more!

Ideally, your goldfish should be kept in an environment with adequate filtration. Just because they can temporarily survive in an environment with inadequate filtration doesn’t necessarily mean they should.

goldfish and guppies in tank
Image By: S-F, Shutterstock

divider-fish Filtration Options

Regardless of the size or shape of the tank your goldfish is living in, there is a filtration option that will help maintain water quality. The most important aspect of filtration is providing an environment that supports the development of beneficial bacteria. These bacteria require oxygen to live, so they will not colonize in an environment without adequate filtration or aeration.

Beneficial bacteria are a necessary part of the nitrogen cycle, which converts dangerous ammonia and nitrite to nitrate, which is less dangerous and more easily managed. If you are not supporting colonization of beneficial bacteria, then you are risking an environment with waste product build up and nothing to relieve it except the reliance on you to perform water changes.

  • Sponge Filters: These are the most simplistic filtration you can use, but they come in a variety of sizes, so they can often fit in small environments like fishbowls. Sponge filters remove very little solid waste from the water, but they function by providing a huge surface area for the colonization of the beneficial bacteria. They are usually used in tanks that hold goldfish babies (also known as fry).
  • Hang-on Back Filters: These are a popular type of filter. They hang on the rim of the tank and have an intake that extends into the water. This intake pulls water from the tank and pushes it through a system that provides multiple types of filtration. HOB filters usually can also provide chemical filtration, which can help with things like unpleasant smells from the tank, and mechanical filtration, which is the type of filtration that will remove solid waste from the tank and collect it in filter floss or a sponge. However, they are usually inadequate for large aquariums, and you might need multiple filters to keep up with your goldfish’s demands.
  • Canister Filters: Usually the most powerful filtration option, canister filters have an intake that extends into the water, but the body of the filter sits fully outside and usually below the tank. A system of hoses pulls water from the tank and pushes it through the filter media within the canister, before returning it to the tank. Canister filters usually contain filter media trays that can be fully customized with the filter media of your choosing. Canister filters are the best option for goldfish.
  • Internal Filters: Internal filters are attached inside the tank on the tank wall and function in a similar way to HOB and canister filters. They pull water in through an intake, push it through filter media, and then return it to the tank. Some internal filters do not provide the space to customize your filter media. These are not a great option if you have fry or other small or weak inhabitants in your tank because they can be difficult to cover the intake. These are not a great option if you have fry or other small or weak inhabitants in your tank because they can be difficult to cover the intake. They also have a drawback in that they take up space within the water, limiting swimming space for your fish. They can also be somewhat cumbersome when it comes to maintenance.
  • Under gravel filters: these are another type of internal filter. As the name suggests, this filter sits under the substrate, pulls water from the bottom of the tank, and returns it to the top once it’s filtered. These filters are not popular with goldfish because they often get clogged. They are very cumbersome to unclog as substrate might not offer easy access to them.
goldfish and guppies in tank
Image By: Tony Stock, Shutterstock


Final Thoughts

It is absolutely necessary to provide your goldfish with filtration, and many animal welfare organizations consider it mandatory. The lack of a filtration system is considered inhumane for goldfish because they are exceptionally messy and produce a very high bioload in aquariums. Poor water quality can lead to illness and even death for your goldfish. There are lots of great options on the market for filtration for a goldfish, even if the environment is small. Investing in proper filtration will help keep your goldfish healthy and happy for years to come.

Featured Image Credit: luckypic, Shutterstock

Our vets

Want to talk to a vet online?

Whether you have concerns about your dog, cat, or other pet, trained vets have the answers!

Our vets

Before you go - Don't miss out!