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How Often To Change Betta Fish Water?

Have you noticed that your betta fish water has gotten dirty or that green algae have begun blooming in your tank’s water and making the tank seem opaque?

Does your beautiful betta seem more lethargic than usual, with its eyes becoming so cloudy that they distract from the vibrant colors of your betta fish?

It may be time for a water change in your tank! Aquarists generally recommend a 20-25% water change every two weeks. However, this rate may vary depending on your schedule and the specific setup of your tank.

If you would like more details on how often to change your betta fish’s water, including what makes you need to change the water so much, read on!

3 ways to change your betta fish water

10-15% change every week

If you are a more dedicated aquarist looking for the optimal way to change the water, it is important to remember that less is more. 

Smaller water changes are better for the water quality’s stability in any fish tank, especially ones containing carnivorous fish such as betta fish. 

More dedicated aquarists recommend changing 10 to 15% of your betta fish’s water every week. 

Luckily, water change is not an exact science. Unless you are a stickler for accuracy, eyeballing the amount of water you remove will do the trick. You are likely in the clear as long as it looks roughly 15%!

25% change every 2 weeks

If you are an average person with a betta fish tank, you may not have the time, patience, or ability to perform a water change every single week. 

In such cases, or in tanks with a larger volume, a 25% water change every two weeks will suffice just as well.

While smaller, weekly water changes are recommended to keep water quality consistent, doing a larger change every other week does not make that much of a difference. 

This may be your preferred option if your tank gets filthy particularly fast. Your fish may appreciate a larger, more immediate influx of clean water!

50% change

There are very rare circumstances where a 50% water change is required. If your betta fish tank is opaque with green algae floating in the water, a 50% change may be in order. 

Obviously, in this case, there will be no set period to repeat this- though it is best to consult an expert so that you don’t have to do it again!

However, if your betta fish is in a tank without a filter, a 50% water change may be required frequently so that the fish does not poison itself by living in its waste. 

Many people opt to keep their betta fish in a filterless tank or even a vase. While most aquarists do not recommend this, a happy and healthy betta fish can be achieved in this manner via regular water changes. 

In most smaller, filterless tanks, a 50% water change will be needed daily. In a larger tank, such as a five-gallon, a 50% water change may be done every two or three days, while a ten-gallon tank may have a 50% change once per week.

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Balancing water changes with tolerance

Balancing water changes with tolerance

Why frequent water changes are necessary

Fish are notorious for producing large amounts of waste- specifically ammonia, which is toxic to most living things. 

While a good filter can help keep your water quality at a high standard, water changes are the best tool for combating the buildup of filth in your tank, as well as the best way to prevent your betta fish from getting ill. 

Water changes can even help your betta fish get healthy faster if it is ill, as this introduces a large volume of fresh, clean water that your betta fish will thrive in.

Smaller changes are better tolerated

Aquarists recommend doing smaller changes more frequently when applicable to keep water quality consistent. 

For most fish, nothing is more important than consistency in water quality. Most fish can even survive through slightly-subpar conditions as long as the water quality remains consistent.

Factors That Affect The Frequency Of Water Changes

Factors That Affect The Frequency Of Water Changes

Size of Tank

The size of your tank will determine how rapidly water evaporates and how often water changes and additions are necessary. 

A larger tank will hold more water, making waste take up a smaller fraction of the water, improving the water’s quality.

Inversely, smaller tanks hold less water, allowing waste to fill the tank even faster. 

In a smaller tank with less water, your betta fish’s waste will have fewer places to go and become denser to cloud the water and provide a more toxic environment for your fish.

Other tank inhabitants

The number of animals in your betta fish tank dictates the amount of waste generated, meaning more water changes may be necessary. 

While smaller inverts such as snails and shrimp produce minimal waste, they can still contribute to the waste of a tank, especially if one dies!

However, the much bigger waste-creators will be other fish. While most people opt to keep betta fish alone, others may choose to keep betta fish with other fish, such as guppies or tetras

Others will keep female betta fish in sorority tanks, which often have a high number of female fish. These high fish counts will produce more waste, necessitating more frequent water changes.

Filter usage

You may need to perform fewer water changes if you have a filter. Filters are usually rated for differently-sized fish tanks, and with a more powerful filter in a smaller tank, the tank’s quality will be kept to a higher standard.

However, a more powerful filter will often come with a more powerful pump, increasing water motion in the tank. 

Betta fish are not fond of high rates of motion, with their natural habitats being ponds and puddles. This means that your betta fish will not be happy with a larger tank, necessitating a smaller filter and more frequent water changes.

Either way, using a filter is far more beneficial than not using one. 

Many people opt to keep their betta fish in a filterless tank. This is not recommended and necessitates extremely frequent water changes- often daily. 

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Thankfully, a filter can minimize how many water changes you need. With a filter in your tank, you may only need to perform a water change once every two weeks!

Adding water

You may need less frequent water changes if you’ve recently added fresh water due to unforeseen evaporation. 

People living in hotter environments will deal with higher evaporation rates, necessitating more frequent water additions. 

When you add new water, it performs much of the same function as a water change, though water has been removed by the sun instead of manually.

How do I change betta fish water?

How do I change betta fish water

Water siphon

A water siphon is the single most trusted tool for water changes and is used by aquarists around the world. 

Manufacturers offer different sizes of water siphons so that aquarists can easily do water changes and vacuum up unsightly algae without having to maneuver a large siphon inside a small tank.

Many different types of water siphons are available, from siphons with manual hand-pumps attached to more streamlined and simplistic designs that rely on gravity and capillary action to move water into your chosen receptacle.

Both of these models have their own advantages and disadvantages. 

For example, a siphon with a manual pump attached may be more work to set up, break down, and clean, but the manual pump allows you to start up the suction of the siphon with minimal effort and no need to maneuver the siphon itself around the fish tank.

On the other hand, the more streamlined siphon designs can be more challenging to use for newcomers but allow for incredibly easy storage and cleaning. 

However, using these siphons is actually incredibly easy when you learn how to do it. 

Simply place the end of the hose in your water receptacle of choice, place the tube diagonal in the tank with its open end facing upwards, and wait until it fills with water. 

Raise the tube out of the water and allow the water to begin to run into the receptacle. 

Once the water has gotten about halfway down the tube, place the tube back into the fish tank, and you have a fully-functioning siphon.

If you are using a siphon to also vacuum up algae, just make sure to vacuum the algae up before the siphon sucks up too much water.


If you don’t want to spend the extra money on a water siphon, simply using the appropriate number of cups may be right for you. 

One advantage of using cups over a water siphon is that cups can be used to find the exact amount of water you want to remove, rather than simply eyeballing the water level like with a water siphon. 

This may require a little bit of math on your end, but you can use the calculated number of cups for the entirety of your fish tank’s lifespan.

One downside of using cups is their lack of suction. While anything near the cup will be sucked in as it is lowered into the water, cups lack the vacuuming quality of siphons that allows siphons to remove algae while also removing water.