How Long Can Fish Live Without A Filter? Few Hours Or A Lifetime?

Jul 18, 2022

How Long Can Fish Live Without A Filter

Image Credit: Tahir MQ (CC License)

A filter is indispensable in a fish tank. There’s no alternative to it. But sometimes, the filter breaks down, leaks, or fails and stops working. This happens to even the best of us. 

But how long can fish live without a filter? A day? A week? Or forever? The answers available on the internet couldn’t be any vaguer. 

So, I decided to step up to the plate and set the records straight once and for all. 

How Long Can Fish Live Without A Filter?

The answer to this question varies depending on the state of your fish tank. If the tank is well-maintained and oxygenated at all times, the fish can go through their entire lives without requiring a filter. 

However, the fish can die within a few hours if the tank is overstocked, dirty, and small. 

I hate to do a hatchet job on anyone, but it is what it is. The article ranking at the first position in Google answers that fish can live without a filter for a minimum of 3 days and a maximum of 7 days. 

But there’s no evidence, research, or even logic behind this claim. Not all fish are made the same, right? Some are more hardy than others. 

No way there’s an exact time frame as to how long the fish can survive without a filter since it depends on how heavily the tank is stocked. 

The more densely the tank is stocked, the faster the toxic compounds will build up. So, a lightly stocked tank will go much longer without a filter than a heavily stocked tank. 

For example, a single betta fish in a 60-gallon tank can go for weeks before its health deteriorates. On the other hand, 4 goldfish in a 30-gallon tank could only go for a couple of days. 

Bottom line – there are so many factors in play that we absolutely can not ascertain how long a fish can live without a filter. It could be a few days, weeks, forever, or a few hours. 

Sometimes, things don’t go as planned. For example, the filter might die on you. It happens to even the best of us. 

Below, I have collected a couple of answers hobbyists shared on different forums on the subject matter. Care going through them?

How Long Can Fish Live Without A Filter? Real Answers By Real People!

“In December, we had a horrible storm that knocked out the power for 10-12 hours, and there were no dead fish.”

“I have had my tank without electricity for at least 24 hours during a power outage. Nothing bad happened. But I did measure the nitrite and ammonia levels after the outage, and they were at 0.”

“In my opinion, they should be okay for at least 12 hours if you rinse the media from the current filter gently and soak it in the tank. This will help to keep ammonia and nitrite levels from getting out of hand.”

“Given that the tank isn’t overstocked and you’re offering aeration and water changes, the fish could live indefinitely without a filter.”

“If you put bubblers in the tank, I think they will be okay for at least a week or so.”

“A lot of people with densely planted tanks don’t even run filters.”

“The answer depends on your stocking level and if you have aeration going on or not. How long the tank’s been set up and what kind of substrate is used also play a part.”

So, you see, there’s no one true blue answer for this question. It solely depends on the tank’s environment. 

But theoretically, your tank’s beneficial bacteria die off after about 30 minutes without oxygen. And, of course, the oxygen is supplied through filtration. 

If the tank’s at 0 ammonia and nitrite levels when the mishap occurred, the fish will likely survive longer even without a filter. 

But if the ammonia and nitrite levels are off the roof, to begin with, the fish can pass away in a matter of a few hours. 

I’d recommend buying an extra filter just in case. They don’t cost much. And it’s always better to err on the side of caution, isn’t it?

I’d also recommend testing the water parameters weekly using API’s Freshwater/Saltwater Master Kit. 

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What Happens When There Is No Filter In The Fish Tank?

A filter is indispensable in a fish tank. It cleans the water of debris, eliminates the toxic buildup of nitrites and ammonia, and aerates the water so the fish can breathe. 

Oxygen Level Depletes 

When you install an aquarium filter, it will circulate the oxygen in the entire tank. If the filter stops, the oxygen circulation will also stop. The fish will not get enough dissolved oxygen. 

This whole ordeal can put the fish through a lot of stress and make life tougher for the fish. 

Algae Bloom 

Algae thrive in still water. When there is no filter in the tank, no current is being produced. Thus, creating the perfect habitat for algae to grow and thrive. 

If the algae bloom gets out of control, it will directly compete with the fish for oxygen and nutrients present in the water column. As a result, the fish will suffocate. 

Increased Toxin Level

Ideally, the ammonia and nitrate levels in the tank should always be maintained at 0 PPM. If there’s no filter, there’s no way the gunk produced in the tank will be safely disposed of. 

As a result, the ammonia and nitrate levels will spike. The fish will then experience red and bleeding gills, increased mucus production, and secondary infections before finally biting the dust. 

Demolished Good Bacteria Colony 

A filter has high oxygen levels, stable water flow, and very little light – 3 of the most essential things beneficial bacteria require to thrive. 

Without a sound filtration system, good bacteria colonies will be eliminated. As a result, the fish waste, organic debris, dead plant material, and fish food will not be broken down. 

Instead, they’ll accumulate and give rise to toxins. 

How Does An Aquarium Filter Work?

To put it simply, an aquarium filter works by pushing water through various kinds of filtration media. The 3 main types of filtration media used in fish tanks are mechanical, chemical, and biological. Each type of filter media serves a unique purpose. 

For instance, mechanical filters work to trap large particles by pushing water through a filter material like a sponge or floss. Next, chemical filters work to extract dissolved waste from the water. 

Lastly, biological filters create an ideal environment for beneficial bacteria to thrive and break down waste. 

Let’s have a brief look at each kind below!

Mechanical Filtration 

Mechanical filtration in a fish tank is achieved by passing the water through a filtration material like polyester floss or foam that can efficiently block the passage of solid materials. 

For example, these solid materials include leftover food, fish waste, and decaying plant material. 

It’s important to note that mechanical filters are not made to break down the waste and process it. It simply blocks and collects the particles. 

Therefore, with these filters, regular cleaning is quite important. If you skip, the filter will get clogged. 

Chemical Filtration 

Chemical filtration in a fish tank is achieved by allowing the water to pass through certain mediums like zeolite and activated carbon that extracts dissolved compounds and waste in the water. 

Since mechanical filtration cannot tackle waste already dissolved in the water, chemical filtration is crucial. For example, zeolite removes ammonia, while activated carbon removes tannins from bogwood, foul odor, dissolved protein, chlorine, and chloramine. 

Naturally, the filter media becomes ineffective over time. Thus, they should be replaced routinely. 

Biological Filtration 

Biological filtration in a fish tank enables the water to pass against a medium like a sponge rich in beneficial bacteria. Beneficial bacteria help convert harmful ammonia and nitrite into less toxic nitrate. 

Biological filtration aids this process by increasing the surface area for beneficial bacteria to grow and thrive on. 

Biological filtration is deemed to be the most important kind of filtration in the tank. Once the ammonia and nitrite are converted into nitrate, it is utilized by plants as fertilizers. 

Types Of Aquarium Filters

The most common type of aquarium filters are sponge filters, hang-on-back filters, and canister filters. Across the world, a vast majority of fish tanks today are equipped with one of these filtration systems.

Sponge filters are most commonly used for smaller tanks like a hospital tank, a breeding tank, or a quarantine tank. Hang-on-back filters are used for small to medium-sized tanks, and canister filters are used for big tanks as they have a much larger capacity. 

Let’s have a brief look at each of them. 

Sponge Filter

Sponge filters are the most simple and inexpensive filters available in the market. It comprises an air pump, a sponge, and airline tubing. 

As the air gets pumped and the air bubbles rise to the top, water is forced through the sponge filter itself. As the water passes through the sponge, small particles are trapped. 

As we discussed above, this is a mechanical filtration system. However, sponge filters are loved more for the utility they offer as a biological filter. That’s because the sponge is an excellent medium to house beneficial bacteria. 

Hang-On-Back FIlter

Hang-on-back filters, also known as power filters, draw water from the fish tank, filter it through a filter chamber and release the water. The pump, lift tube, and filter chamber are all merged into one system. 

You simply have to hang the filter on the tank’s edge, insert a filter cartridge in the chamber, and plug in power. 

When the water passes through the filter cartridge and debris is trapped, the water will be mechanically filtered. Even better, these filter cartridges come with a pouch where you can add activated carbon for chemical filtration, which removes toxic impurities and odors. 

Lastly, as the water moves through the filter chamber, the filter medium is continuously oxygenated – enabling beneficial bacteria to grow and do their thing, AKA biological filtration. 

Canister Filter 

A canister filter is an external filter meant to be placed below the aquarium, connected by tubes. A water intake is built in the tank, and water is pulled into the canister, which houses filtration media. 

Once the water is in the canister, it goes through a series of chambers, including biological, mechanical, and chemical filtration media. 

After that, the water is sent back to the tank through a tube. A pump is installed over the sealed canister, allowing water to flow through the filter media.

Canister filters are useful for big aquariums, ranging from approx. 50-200 gallons. What I like the best about these filters is that they can hold a lot of filtration media. 

Frequently Asked Questions

Before we end this article, let’s look at some of the frequently asked questions on fish and filters. 

How Long Can Goldfish Live Without A Filter?

Goldfish can live without a filter for anywhere between a couple of days to a few weeks. Goldfish are quite messy. They poop a lot. Therefore, the water gets polluted easily. 

So, you must add a proper HOB or canister filter to your goldfish tank. A sponge filter is not powerful enough for goldfish. 

How Long Can A Betta Fish Go Without A Filter?

The answer is the same – anywhere between a few days to a few weeks depending on how densely the tank is stocked and the condition of different water parameters. 

I came across several fishkeeping websites claiming that bettas can live without a filter. Yes, they can, but for how long?

Their lifespan will be significantly compromised. 

How Long Can Angelfish Live Without Filter?

Angelfish are extremely sensitive to changes in their environment. Therefore, they cannot live for a long time without a filter. 

From what hobbyists shared on social media, angelfish can live for only around 12 hours without a filtration system. 

Can Platy Fish Live Without A Filter?

Platy can live without a filter if the tank is lightly stocked, there’s enough oxygenation and plants, and the water is clean. 

However, I’d still recommend getting a filter. If you have a small tank, a sponge filter will do. 

How Long Can Tropical Fish Live Without A Filter?

Most tropical fish are hardy. However, they’re all vulnerable in the absence of a filter. Based on the tank’s situation, they can go on without a filter for anywhere between a few days to a few weeks. 

That being said, I know some hobbyists who don’t use a filter at all. But bear in mind that their tanks are heavily planted. 

I’d strongly recommend getting a robust filter for your saltwater tank. 

Final Words: How Long Can Fish Live Without A Filter?

A fish can live anywhere between a few hours to a lifetime without a filter. It all comes down to the tank’s environment. Of course, if the tank is big and lightly stocked, the fish can go for longer without a filter. 

However, if the tank is overstocked and polluted to begin with, the fish may breathe its last in a span of a few hours. 

All in all, filters are indispensable for a fish tank. There are different kinds to choose from depending on your tank’s needs and your budget. 

Recommended Readings!

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rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.