Should Aquarium Filter Always Be On?

Should you always leave your aquarium filter running? Many fish owners wonder about this. In this article, we’ll explain why it’s important to keep your filter going all the time.

The filter does important jobs to keep your fish healthy. We’ll talk about why it’s best to keep it running and what could happen if you turn it off. Understanding this helps make sure your fish stay happy and safe.

Should aquarium filter always be on?

The answer is yes, aquarium filters should generally remain on continuously for several reasons.

Why Should the Aquarium Filter Always Be On?


Aquarium filters are really important because they help keep the water in the tank fresh for fish to breathe. They do this by letting oxygen from the air get into the water and letting carbon dioxide out.

This is super important because fish need oxygen to breathe just like we do. If the water doesn’t have enough oxygen, the fish could get sick or even die.

So, filters are like the lungs of the aquarium, making sure the water stays clean and healthy for the fish.

Filters help increase oxygen levels in a few ways. First, when the filter pushes water out, it makes ripples on the surface, which lets more water touch the air. This helps swap gases like oxygen and carbon dioxide.

Second, as water goes through the filter, it gets in contact with bubbles or surfaces that have lots of oxygen, so the water can soak up more oxygen.

Lastly, filters keep the surface of the water clean by removing gunk, which could stop gases from getting in and out of the water.

Water Circulation

Aquarium filters also help keep the water moving around in the tank. This is really important because it helps spread heat, food, and air evenly everywhere in the tank. When the water moves, it makes sure that all parts of the tank get what they need to stay healthy.

If the water doesn’t move enough, some areas might become still, which could make the temperature change, the food not spread out properly, and the air levels drop. So, filters keep the water flowing smoothly to keep the fish and other creatures happy and healthy.

Filters use pumps to move water in the tank. They pull water from the tank, pass it through the filter to clean it, and then push it back into the tank. This keeps the water moving all the time, which stops waste and dirt from gathering in one place.

The moving water also helps keep the temperature and pH level the same everywhere in the tank. So, filters keep the water clean and the environment stable for the fish and other creatures by making sure everything mixes up well.


Keeping the filter working well is super important because it stops problems like too much ammonia, nitrite poisoning, and too many algae from happening.

These issues can make the fish sick or even harm them. Filters get rid of waste and harmful stuff, so the water stays clean and safe for the fish to live happily.

Biological Balance

Filters are really important for keeping the balance in the aquarium ecosystem just right. There are good bacteria that live in the filter and around the tank. These bacteria help break down waste from the fish and other stuff in the tank.

They change harmful stuff like ammonia into less harmful stuff called nitrate. This process is called the nitrogen cycle.

Nitrate can build up over time and cause problems for the fish if it’s not taken out with regular water changes or used up by plants in the tank. So, filters help keep the ecosystem in the tank healthy by managing these bacteria and their work.

Filters are like a cozy home for good bacteria. These bacteria need a lot of space to grow and do their job, which is breaking down harmful stuff like ammonia and nitrite in the water. This helps keep the water safe for the fish and other creatures in the tank.

So, keeping the filter running all the time is really important to make sure these bacteria stay happy and keep the tank’s water clean and healthy.

Risks of Turning Off the Aquarium Filter

Oxygen Deprivation

When you switch off the aquarium filter, the water stops moving around as much, which can make the water still. This stillness can cause problems because it stops gases like oxygen and carbon dioxide from swapping properly at the water’s surface.

Fish need oxygen dissolved in the water to breathe, just like we need air to breathe. If there’s not enough oxygen in the water, the fish can get stressed out, have trouble breathing, and even die.

So, it’s really important to keep the filter running to make sure the water stays fresh and the fish stay healthy.

When water doesn’t move much, oxygen levels can drop quickly, especially in tanks with lots of fish or plants that use up a lot of oxygen. If there’s not enough oxygen, fish might start acting strange, like gasping for air at the surface or seeming really tired.

This shows they’re not getting enough oxygen to breathe. If they’re stuck in low oxygen water for a long time, their immune systems can get weak, which makes them more likely to get sick or stressed out. So, it’s crucial to make sure the water stays oxygenated enough to keep the fish healthy and happy.

Increased Toxin Levels

The main job of an aquarium filter is to clean the water by getting rid of harmful stuff like toxins and waste. When you switch off the filter, it stops cleaning the water.

This means toxins like ammonia and nitrite, as well as waste from the fish, can start to pile up in the water. Too much of these bad things can make the water unhealthy for the fish and other creatures in the tank.

Ammonia is made when fish poop and other stuff in the tank break down. Even a little bit of ammonia can really hurt fish.

Another harmful thing is nitrite, which forms when good bacteria break down ammonia. Both ammonia and nitrite can make fish really sick.

They might have trouble breathing, not want to eat, and be more likely to get sick from infections. So, it’s super important to keep these toxins low in the tank water to keep the fish healthy and happy.

When there’s no filtration, waste from fish and other things in the tank builds up. This waste is like food for bad bacteria, which can grow a lot and make more toxins.

These toxins make the water even worse for the fish. Without the filter cleaning up the waste and toxins, the tank’s balance gets messed up. This makes it more likely for the water to become unhealthy and for the fish to get sick.

So, keeping the filter running is key to keeping the tank’s ecosystem in check and the fish safe from harm.

Altered Biological Balance

Aquarium filters are really important for keeping the tank’s ecosystem in balance, especially by managing something called the nitrogen cycle. Good bacteria live in the filter and other parts of the tank.

They help change harmful things like ammonia and nitrite into less harmful nitrate. This process, called biological filtration, is crucial for keeping the water safe and healthy for the fish.

When you switch off the aquarium filter, the whole process of biological filtration stops. This messes up the nitrogen cycle, which can cause ammonia and nitrite levels to shoot up.

High levels of these toxins can seriously harm fish, causing burns, breathing problems, and damage to their organs.

Plus, when the nitrogen cycle gets disrupted, it can make it hard for good bacteria to do their job, making water quality even worse.

Not having the filter running also means the water isn’t moving around as much. This can lead to still areas in the tank where bad algae can grow fast. Too much algae can take over the tank, starving fish and plants of the things they need to live and making the tank look gross.

In short, turning off the aquarium filter is really risky for fish health and the whole tank’s stability. It can lead to less oxygen, more toxins, messed-up nitrogen cycles, and too much algae. Keeping the filter going all the time is super important for keeping the water clean and safe for the fish.


This article explained why it’s essential to keep aquarium filters on all the time. It talked about how filters help fish tanks by adding oxygen, moving water around, cleaning out harmful stuff, and keeping the environment balanced for the fish. It showed how important filters are for keeping aquatic creatures healthy.

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