Why fish tank needs a filter A fish live without a filter for a maximum of seven days and a minimum of three days. A filter helps clean the water over and over again, so the toxins in it don’t settle down. But that doesn’t make the filter a necessity for fish survival. We discussed the matter with our team of fish experts and gathered for you all the things you need to do in order to keep your fish alive and healthy even without a filter.

How Long Can a Fish Go Without a Filter?

As we mentioned earlier, the maximum a fish can go on living without a filter is seven days and the minimum is three days.

Moreover, the possibility of a fish living fine in an aquarium without filter is pretty high as they can adapt to any environment relatively quickly. But the period it can go on without the water purifying constantly depends upon some factors.

These include the kind of fish under question, the quantity of fish in your aquarium, the acidic and bacterial level of the water, other filtration methods, and the resources you have to offer.

Function of a Fish Filter

A fish filter performs two basic functions, cleaning the dirt and debris from the tank and flowing oxygen. When the filter performs cleaning actions, that process is called a cycle. But if you can’t spend the required money for a filter and you need your aquarium to work without it, there are a couple of things to be taken care of.

Oxygen Circulation

Fish tank without a filterThe first thing you would tell yourself in a situation where you have no purification system would be that fish survive without filter. And the justification you would give yourself would be that fish live in ponds and rivers too they don’t need a filter there. The water they get is enough for them to breathe in and survive.

However, that’s not true: fish survive in water by obtaining oxygen from it. Moreover, no one would like breathing in an unfiltered, polluted atmosphere. Fish are found in oceans and rivers as the water constantly keeps circulating and provides a natural environment.

When you attach a filter, the oxygen circulates in the entire tank. And when the filter stops, the circulation stops as well. Since the oxygen supply is only available at the bottom-most level, fish begin moving towards the surface to breathe. However, this entire condition can put a fish under a lot of stress and make it challenging for a fish survive without oxygen.

Water Filtration

Your water filter is responsible for providing adequate water movement throughout the aquarium since the proper water flow is of great significance. Water filters come in variations of water flow and the powerful ones offer a more robust flow, whereas the ones that work fine have a regular flow. Most fishes cannot handle high water flow, and it might eventually become a threat to their life.

Benefits of Good Water Circulation From Fish Filter

Before we move on to which water flow is best, let’s see the benefits of good water circulation first. These are as follows:

  • Adequate circulation ensures the same temperature throughout your water tank. Also, with the help of the aquarium heater, it keeps the temperature moderate for the fish to survive.
  • Some aquarists, like a reef, are dependent on the water flow for providing food and eliminating the gunk accumulated. Even in the case of aquatic plants, they need good circulation to produce carbon dioxide.
  • The tension created in the aquarium due to the filter helps transfer more oxygen to water. This increased amount of oxygen is the reason why your fish might seem healthy and playful.
  • Water flow is also crucial for the living bacteria to help them become stronger, keep steady and prevent nitrite and ammonia from exceeding a certain level.

Some fishes actually feel energetic and happy by swimming against a strong water flow.

Flow Requirements For Filters

The next question that comes to your mind would be the flow requirements. The answer to this is somewhat tricky because what water flow you need to provide depends on the type of fish, aquarium, and resources available.

If you have a large aquarium with plenty of fish, a strong water flow might be the best for your situation. But if you notice your fish fighting against the current to remain in one place, you might want to make some changes.

Fish like goldfish, betas, or guppies are more inclined towards a smooth flow.

Ammonia Buildup

How long can fish go without a filterAnywhere there is a fish there is bound to be ammonia, and ammonia buildup in an aquarium has proven to be highly deadly for these creatures. It can significantly reduce the fish’s life and weaken it. Let us put it like this, you need two odds to get an even, so to deal with the released ammonia, you need to add a substance that would kill it.


Ammonia in the tank calls for adding live bacteria in the water tank. The bacteria make a home in the water filter and begin to breed there. As they live on, they consume ammonia and produce nitrite in turn.

But nitrite is just as toxic for fish as ammonia is, so another set of bacteria is added to the filter that cancels out the nitrite and gives out nitrite; hence, the water cycling. However, you should make sure your aquarium has sufficient bacteria growth before you put your fish in the water tank.

The filter here plays an important role now as it primarily helps with circulating oxygen, cleaning the water of debris, ammonia and nitrite buildups, and other toxic constituents. Once it stops working, the bacteria in the aquarium are instantly affected and start expiring.

Since the ventilation system in the water tank won’t be good enough at that time, you will find the fish moving upwards to inhale some air.

Will a Fish Tank Work Without a Filter?

Having a filter system is essential but not necessary. Let’s understand that from the perspective of a pond or water area. Every lake in this world is large enough to accommodate plenty of fish and balance the aquatic ecology.

Unhygienic Atmosphere

The fact that lakes are large enough to make sure fish live healthy lives full of oxygen means that the waste and the toxic chemicals released are dissolved, and the water is safe for fish. On the other hand, aquariums offer the same thing only through an artificial process and need a lot of resources to make them look alike. If the water remains unchanged, it will become filthy and destroy the lives of all fish.

A fish tank without filter would work fine. But even if you replace it by changing the water two times per day and your aquarium has plenty of fish, the water will not be hygienic.

That’s because the living bacteria are not powerful enough to cancel out the increased production of ammonia and nitrite. This could result in the untimely death of the fish.

Rule of Thumb When It Comes to No Tank

Some fish can live in unfiltered water for an indefinite amount of time if the aquarium has a large number of plants in it. The rule of thumb is that fish caught from rivers or streams cannot live without filters because they do not get enough current to acquire the oxygen needed. Whereas, fish obtained from ponds or lakes are well off without filters.

Which Fish Can Live Without filters?

Different fish have different water requirements, so their life without filter depends upon their kind. Some fishes that don’t need filters are:


It is one of those fishes that are highly dependent on their environment and change according to the circumstances. Goldfish prefer to live indoors in winters and thrive in outdoor ponds in summers. A considerable variation of goldfish can survive in filterless tanks and for long periods. Also, Goldfish only grows as big as the aquarium is and no more than that.

White Clouds

The most moderate kind of fish, discovered in the mountains of China, white clouds are brownish-silver in color. Their maximum length is known to be one to one and a half inches only, so they can live happily in a small tank that has no filters. And the best part is that white clouds can live a complete, long, and healthy life in only two gallons of water, sometimes even less.


Betas are known for their love for large tanks, and since they are only two to three inches long, their survival chances in tanks without betta filters are pretty high.


By now you must have understood all the ways and timelines on how long a fish can go without water. Let’s sum everything up, so nothing is left out:

  • Can fish tank be without a filterFish can survive without water for about three to seven days, but that mostly depends on the kind of fish we are talking about
  • Filters are used for keeping the atmosphere of the aquarium clean
  • The ammonia and nitrite buildup in the water tank can kill the fish if not eliminated in time
  • The living bacteria dies in no more than thirty minutes of the filter supply being cut off
  • Some fishes can live without a filter for extremely long periods of time

That being said, our article comes to an end. We hope this article has helped solve your problem and has encouraged you to be cautious about leaving your fish without a filter.

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