Do Goldfish Need a Filter? What you need to know…

I once left a pet goldfish tank in the care of a friend for a week. Little did I know that they weren’t aware of my tank’s filtration system cleaning schedule, which left undone and meant that my poor fish were soon swimming in toxic chemicals, waste and algae!

I was able to get things under control with a well-timed water change and gained some insight into who to trust with my fish.

If we want our goldfish to live a long and healthy life, one of the first components is to maintain water quality and keep their tank clean.

If you’ve ever had a similar situation or asked the question “do gold fish need a filter?” read on for the answer to this and many other questions regarding goldfish tank filtration!

Can Goldfish Live Without a Filter?

Goldfish Swimming
Goldfish Swimming

No, they don’t need one provided that they have clean water.

However, given the fact that goldfish are widely known to be quite a messy fish that produces a lot of waste it can take a lot of work to keep dirty water from becoming a problem.

This is where using filters can come in handy in maintaining goldfish health.

Longest Living Golfish

If you need proof of the fact that goldfish don’t technically need a filter, consider the following: Guiness Book of Records named Tish the longest-lived goldfish as an astounding 43 years of age, and she lived in a simple fish bowl without water movement or added filters! So do goldfish need a filter? Technically no!

Home Conditions Versus Open Waters

In the wild, this goldfish waste has tons of space to disperse and is therefore a non-issue.

This means that a natural ecosystem won’t need a filter, whereas one that we create at home will.

The problem with waste accumulation comes in when we confine our goldfish to smaller spaces such as traditional tanks or goldfish bowls. Can goldfish live in a bowl? It depends, but its still best to provide your pet with the ideal conditions for them to thrive.*

NOTE

Another nice thing that our hypothetical wild goldfish keeper wouldn’t need to worry about is the water bill!

Why Are Filters Good For Goldfish?

Filters are great for keeping goldfish! Not only do they help ease the process of keeping the water in your tank clean and free of ammonia while simultaneously aerating it and infusing it with oxygen.

NOTE

Without a filter, you’d need to potentially need to perform water changes much more often than otherwise, as much as 50% of the tank water per day in some instances!

These handy devices can help make regular water changes much less of a chore

These handy devices can help make regular water changes much less of a chore.

How Do Filters Work?

That being said, even the most powerful filter will not actually remove solid particles from the tank itself.

The filter system works to trap solid particles so they do not break down and raise the ammonia levels in the tank as quickly as they would otherwise.

NOTE

It is up to the actual fish keeper themself to then remove the waste-filled filter media and clean it, thereby taking solid waste out of the tank.

Here’s an informative video of the role of filters in an aquarium

How Does an AQUARIUM FILTER Work

While there are many different varieties and brands of filter out there, they all act on the same basic principles

They use some form of energy to pull water through the filter itself with enough force that solid matter is trapped in the filter media, where it is trapped and held.

Types Of Filtration

When we think of filtration we may immediately leap to thoughts of complicated canister filters and eternal filters, but there are actually several different forms of filtration active in your goldfish tank at any one time.

Biological Filtration & Beneficial Bacteria

There are many varieties of beneficial bacteria that perform a valuable service for our fish tank.

These beneficial bacteria act as a form of biological filtration, breaking down the ammonia and nitrates that are released from the breakdown of goldfish waste, uneaten food, and dead organisms.

Tank Prep

Setting up a new tank comes with the additional first step of setting up this biological filter system as well!

Rather than just putting all of the goldfish, plants, and decorations in at once, the proper technique is to allow time for beneficial bacteria to establish themselves.

Nitrogen

Adding in a source of nitrogen such as pet food or even a used filter form another tank can jump start the process, giving these good bacteria time to begin fixing nitrogen.

This allows the nitrogen cycle to be up and running in your tank well before the goldfish enter, preventing immediate shock from harmful conditions in the tank.

Chemical Filtration

As the name suggests, chemical filtration works by introducing a filter media that chemically bonds with and removes nitrates and other waste chemicals.

The two primary methods of chemical filtration are using activated charcoal and specifically formulated resins.

NOTE

While these are not often used as the first line of defense, chemical filtration can work wonders when you notice that ammonia and nitrite levels have risen rapidly due to feeding or new goldfish in the tank.

Mechanical Filtration

Based on using a form of technology (usually a water and air pump) to assist with water movement through, mechanical filtration includes both internal filters and external filters.

These terms describe their positions relative to the tank itself, either outside or inside of the aquarium.

NOTE

Many pet stores sell full aquarium kits, complete with all of the mechanical filtering you may need along with some decoration to get you started.

Advantages of Mechanical Filtration

The nice thing about mechanical filtration is that it is easily visible and can be cleaned and maintained, unlike chemical and biological filters which run more on unseen chemical reactions.

With an external filter, you can typically see all of the moving parts as well as the filtration media, allowing you better insight into when it may be time to change or clean it.

What Kind Of Filter Works Best for Goldfish?

Planted Aquarium with Sponge Filter
Planted Aquarium with Sponge Filter

A good bet is to work with a combination of biological and mechanical filtration for your goldfish tank.

This can mean attaching an external filter to provide additional gas exchange with more air movement, or an undergravel filter which moves the fine material through the substrate of the tank.

Check your local store

A good rule of thumb is to see what’s in stock at your local pet store, as they’ll likely have replacement parts and additional filtration media when you need it down the road.

They’ll also be able to help with what they may recommend for goldfish that you’ve purchased from their specific breeders.

Types of Filters

There are a variety of mechanical filters available on the market, and it’s up to you to decide which works best for your style of fish keeping.

Some internal filters may be more obtrusive and take up additional space inside of the tank, which is an important consideration when keeping goldfish in a small tank.

Canister Filters

These external filters sit underneath your tank itself, requiring a tank stand in order to function properly.

They use gravity to pump water downwards into the filter, which then moves filtered water back up and into the tank.

Canisters can make for a great option when working with small tanks. The filtration occurs outside of the tank, meaning more room for biological filtration in the substrate along with swimming space for your goldfish.

Sponge Filters

A bit more challenging to use with goldfish than other filters, these act in combination with an air stone to draw water through an internal sponge.

Considering that goldfish especially need a filter to deal with large amounts of waste, this may not provide enough filtration on its own to be the sole component of your system.

Hang-on Back Filters

Also referred to as HOB filters, these are a type of external filter that sits on the top of your tank (or “hanging on the back” of it).

They work similar to a canister filter, but rather than using gravity they utilize an air pump to pull water up into the filter media.

After this point the water is distributed back into the tank via dispersal.

Gas Exchange

The benefit to this is that the water disturbance at the surface creates additional gas exchange of carbon dioxide and oxygen for your tank, allowing for more oxygen to be dissolved than if the water were simply still.

NOTE

As an added bonus, the external nature of this filter means it works well in combination with others either inside or outside of the tank.

Play around with what works best for your tank, as there are few wrong answers when it comes to combating poor water quality!

What Size Filter Do You Need For Goldfish?

Goldfish Swimming at the Bottom of the Tank
Goldfish Swimming at the Bottom of the Tank

For a tank with goldfish, I recommend looking at a filter with at a minimum four times the water volume of the tank itself. That would mean for a typical 30-gallon tank you would want a 120 gallon per hour capacity filter in order to keep up with the amount of waste in the tank.

How To Maintain A Goldfish Filter

While the type of maintenance depends largely on which filter you’re using, with proper care you can make a good filter last much longer than it would otherwise.

One odd reality of filter cleaning is that you also don’t want to clean them too thoroughly or too often, as this can interfere with the beneficial bacteria that accumulate on the filter media and throw off the ammonia reduction power of the tank.

How Often Should You Clean Your Filter?

Canister Filters

Since these are largely enclosed, these are fine with 3 to four months between cleanings.

Hang On Back Filters

Once a month at a minimum, which can also be a good time to replace the filter media.

Sponge Filters

Every two weeks or so should ensure that these are working at their best.

Undergravel Filters

Seeing as it is buried underneath your substrate this one can be a bit trickier to get to, I recommend regular vacuumings every two weeks or so.

What To Do If You Don’t Have A Filter

Goldfish Bowl at a Beach
Goldfish Bowl at a Beach

If you’ve decided to go the tiny bowl route without a filter, there are a few key actions to take in order to keep water parameters healthy for your goldfish.

These are mainly aimed at ensuring clean water and that there is enough oxygen in the tank, as these are the first things to go in a closed tank system.

Don’t Overstock

Along with the issues of crowding, having too many goldfish eat and poop in one tank can lead to a lot of waste.

As this begins to break down inside of your tank, it can rapidly spiral into toxic levels and lead to getting your fish sick.

Simply put, if you’re looking to put more goldfish in the tank, your goldfish needs a filter.

Water Cycle

Regular water changes are critical whether you have a filter or not.

You’ll want to change at least 15% of the tank’s water each week.

Plants

Adding live plants can be a great way to boost the oxygen levels in your tank.

These natural elements can add a visual pop to any tank, but it should be noted that the notorious goldfish eat many varieties of plants.

I recommend Anubias or Java Ferns as ones most fish won’t eat.

Check Your Goldfish Tank

Use an aquarium test kit to keep an eye on the chemical water parameters, but also keep a good eye out for any brownish discoloration or sediments floating in the water.

Ammonia levels above 0 parts per million mean it’s time for a water change!

Can Goldfish Live In Tapwater?

Goldfish can live in tap water, assuming that it’s been treated with a water conditioner first.

Many cities have additional chemical components that may be harmful to the good bacteria in your tank, such as chlorine and fluoride.

A water conditioner acts to buffer these out of the water in the tank.

Conclusion

Throughout today’s article, we’ve answered the question of “Do goldfish need a filter?”

In some cases where water is being changed enough and oxygen is adequate, they may not. However, in order to keep up with the amount of waste they are capable of producing I highly recommend looking at a good filter to keep your fish safe and make things easy on yourself.

Feel Free To Share!

As always I hope that this post “Do goldfish need a filter?” has helped to solve some of your goldfish filter questions.

Feel free to share this with any other goldfish fanatics you may know, and I wish you the best of luck on your aquarium adventures! You also might want to read the Do Goldfish Need a Bubbler article.

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Mollie Newton
Mollie Newton
Founder of PetMeTwice. I love all types of animals from fish to fluff-balls! I also enjoy writing short stories and helping train animals 🤩