How Long Can a Betta Fish Go Without Water Change?

green betta fish

Betta fish are known for their resilience. They can withstand environmental toxin buildup, and other issues a tad better than most aquatic pets. But your pets need water change to thrive.

Betta fish can go up to 3 to 4 weeks without a water change. But if you delay changing the water every so often then your Betta fish will suffer. Dissolved Organic Compounds and toxin buildup will cause illnesses and deformities if your betta experience frequent exposure.

It’s better to adopt a frequent water changing habit and know how to properly change your tank water. Without proper knowledge and handling, your betta will suffer and potentially die.

Read the rest of this article to know about water change, and what happens if you don’t do it routinely in detail.

What Happens If You Don’t Change Your Betta Fish’s Tank Water?

Many factors determine what happens if you don’t change out your Betta fish’s tank water.

  • Size of the tank.
  • Presence of a filter.
  • The number of fish.
  • Presence of food and excrement.

The size of your tank mostly determines how long your Betta fish can go without a water change. The bigger the tank, the longer your Betta fish can survive. More water in your tank means the dilution won’t be too concentrated, and there’ll be more Oxygen for the fish to breathe.

For fishbowls or small tanks, your Betta fish will barely make it till a week and a half without a water change.

For any larger tanks, your Betta fish can survive from 2 to 4 weeks without a water change.

A filter is another important factor when considering your Betta fish’s survivability. With a filter, it will reduce DOC buildup, and introduce oxygen into the system if it is mechanical. The fish can breathe better, and the tank water won’t be easily contaminated. Without it, you’ll have to take off roughly a week from your estimates about the Betta fish’s survivability.

Depending on how many fish reside in the same tank as your Betta fish, their survivability will vary. A lone Betta fish will have more resources and Oxygen. While a Betta fish living with other fish will have to share and suffer sooner.

If you’re overfeeding your Betta fish, they’ll leave extra food discarded. They will also produce waste. Both create Ammonia buildup in the tank. This is extremely harmful to your Betta fish.

Fortunately, bacteria living in the tank can absorb and break down Ammonia. These bacteria will produce Nitrate, a far less harmful substance. But if it builds up too much, it can still be deadly.

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Your Betta fish won’t be able to survive Ammonia or Nitrate saturated water for long. With contaminated water, your Betta fish will suffer and contract diseases within the week.

Can I Fill Up the Tank With Tap Water?

It would be convenient if you could fill up your Betta fish’s tank with tap water. But using tap water comes with a few caveats.

Tap water isn’t optimal for your Betta fish. Tap water contains many contaminants and particles that can harm your Betta. The damage isn’t immediately noticeable either, since you’re introducing chemicals that build up over time.

There a quite a few harmful compounds in tap water. I’ll be mentioning the major culprits that you should watch out for.

Chlorine and Chloramines

The most common chemical element and compounds found in tap water are Chlorine and Chloramines. Water comes from various sources, and it can also become contaminated while traveling through the pipes. These chemicals are put into water to disinfect it.

These chemicals are mostly harmless to humans. But they can poison your Betta fish’s blood and gills.

Inorganic Compounds

There are also Nitrates, Nitrites, Copper, Fluoride, and Phosphates present in tap water. Tap water can contain each of these up to 1 ppm, especially Nitrate up to 10 ppm. These amounts will be mostly harmless to your Betta fish. But they can be the trigger for some major health concerns.

For Nitrates, these will build up from the eating and excretion habit of Betta fish in the tank. If there’s additional Nitrate in the tank, then it can cause Nitrate poisoning.

Nitrate poisoning can trigger with only 20mg Nitrate per liter in the water. Your Betta fish will show few symptoms early and will die by the time you spot severe issues. You can spot some of these early signs.

  • Appetite loss.
  • Appearing stunned or dazed.
  • Lying motionless on the bottom of the tank.
  • In the last stages, the Betta fish will curl into itself.

Copper is not as directly harmful, but its effects are even more silent than Nitrates. If your tap water already contains trace amounts of copper, you may have trouble medicating your fish.

Copper Sulfate is a commonly used treatment for Betta fish. But if you already have copper in the tank, it can lead to a lethal overdose. Especially if your plumbing is done with copper pipes. This can lead to significantly high copper levels, poisoning the fish.

Copper levels at or above 25 ppm will cause these issues for your Betta fish.

  • Hindering growth.
  • Reducing reproduction.
  • Altering brain function.
  • Reducing enzyme activity.
  • Altering blood circulation and chemistry.
  • Reducing metabolism.
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With higher doses, your Betta fish will gradually die.

Phosphate will not directly affect your favorite pets, but it will accelerate algae growth in the tank. So, you’ll have to contend with an additional issue in your tank.

Thankfully, you can just use an aquarium water conditioner to get rid of all these compounds. You can continue using tap water without worry once you use a product for conditioning it.

How to Use an Aquarium Water Conditioner

You can use a conditioner for these cases.

  • Setting up a new aquarium.
  • Changing water.
  • Introducing new fish.

You can use 5ml per 10 gallons, or 15 ml for 30 gallons of water in your tank. Of course, make sure to read the label of whichever conditioner you buy and follow the instructions.

What Kind Of Water To Use For Betta Fish

What if My Betta Likes Dirty Water?

Some owners suspect that their Betta may like dirty water. They claim to see their male Betta fish make bubble nests in dirty water more than clean water. As bubble nests are associated with a comfortable male Betta, the owners make the connection.

However, this is a wrong assumption. Betta fish will build bubble nests in freshwater too. But the agitation of moving water, and the quality of water will pop the bubbles. Whereas dirty, stale water will sustain it and gas buildup will cause more.

Also, many theorize that the Betta fish creating bubble nests in dirty water isn’t happy. The dirty water probably triggers their survival instinct. They make nests frantically to ensure they can have offspring.

Can I Use Bottled Water for My Tank?

Bottled water, or bottled spring water, is a costlier option to tap water. But if the pH level of the water is between 6.5 to 7.5, then it is the ideal alternative. The water already contains the minerals and nutrients necessary for your Betta fish. You can use a stress coat conditioner to ensure the water is optimal.

Distilled water also falls into the category of bottled water. However, it‘s the worst choice.  All minerals, nutrients, and chemicals have been removed from it.

If you use distilled water, your Betta fish will get no minerals it needs to survive. Your pet would lack energy, lose its color, and potentially die.

You can also get pre-treated water specifically for your Betta fish. Betta fish water comes with the exact pH level, minerals your Betta fish needs. Aside from the hassle-free aspect, such water is more affordable than bottled spring water, considering the cost of the conditioner.

What About Water From Natural Sources?

You can also consider water from natural sources, such as well-water and rainwater. The water from these sources is not conditioned. So, you might assume these options are safe.

This doesn’t hold water for well water. Well-water can contain phosphates and highly dangerous toxins. This happens mostly in rural areas, where farmers use pesticides.

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Well-water can also contain dangerously high levels of heavy metals and Arsenic. You’ll likely have to use chlorine to get rid of these issues and then a conditioner. Using well water will increase your cost severalfold.

Rainwater can be a much safer option. If you can store a lot of it, then you can consider using it. But there are a few things that you cannot control and should watch out for.

  • Rainwater typically won’t contain contaminants. But if your city suffers from air or water pollution, it’s likely unsafe.
  • The water is mildly acidic and contains no chemicals to counter it.
  • Rainwater’s TDS or Total Dissolved Solids is next to zero.

You can theoretically use Rainwater only for your tank, as wild Betta can live in it. However, it’s better to use an initial mix of 25% of rainwater to tap water. Proceed to use 50% only if the following conditions are met.

  • Rainwater pH is around 5. If you measure the pH of the mixed water and do not find it below 6.5, you can proceed.
  • Condition the tap water you’ll be mixing in.
  • The hardness level of water isn’t too low.

The safest method for choosing water is to take a sample to your local pet store. They most likely will have a testing kit and check your sample free of charge. You’ll know if your water source is safe for your Betta fish.

How and When Should I Change My Tank Water?

Regardless of any factors, you should change your tank water weekly. You may have a filter and an Oxygen pump in your tank, but it’s better to not put extra stress on them. You can also track your Betta fish’s reaction to the water change and adapt faster.

Smaller tanks will need larger volume changes. DOC and toxin buildup happens faster and becomes concentrated in small tanks. Large tanks take longer to have such issues.

For water change, you can follow some general directions.

  • For small tanks of 5 gallons or so volume, change 40% to 50% water.
  • For tanks with 10 gallons or higher, change 20% to 30% of water.
  • If you have a large tank with a filter, then changing 15% of the water is sufficient.

Using a mechanical filter will provide your Betta fish with moving water, which slows algae buildup and promotes Oxygen saturation.


Understanding water sources, composition, and water change are important for keeping Betta fish. Just by managing your tank water, you eliminate chances of diseases, toxin buildup, and other health complications. This way, you can offer your Betta fish a healthy, happy life at minimal cost and effort.

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Muntaseer Rahman

About Author

Hello, I’m Muntaseer Rahman, the owner of I’m passionate about aquarium pets like shrimps, snails, crabs, and crayfish. I’ve created this website to share my expertise and help you provide better care for these amazing pets.


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