How Often Should You Change Water In A Betta Tank?

How Often Should You Change Water In A Betta Tank

Changing water is crucial for any aquarium fish. Many fish keepers have the misconception that bettas are hardy and they don’t need regular water change. This is absolutely wrong. No matter how hardy a fish is, it can’t endure constant ammonia buildup in a confined space. So, if you are not changing water regularly, your betta fish is going to die at some point.

If the tank is less than 5 gallon, you need to change 40% to 50% water every week. For tanks bigger than 5 gallon, you need to change 20% to 30% water weekly. If the tank has proper filtration, changing 15% water every week is enough.

There are lot more to know about changing water in a fish tank. The frequency of water change actually depends on many factors. In the rest of the article, I’ll go over each of these factors in details.

Relation Between Tank Size & Water Change

In the second paragraph, I have mentioned to do larger water change in smaller tanks. Why is that?

To understand the relation between water change and the size of the tank, we actually need to know why we are changing water in the first place. Let’s start with the basics.

When we keep any fish in the aquarium, naturally it produces waste. Also, we regularly feed the fish. Some food particles remain uneaten. All these organic materials create ammonia in the aquarium.

This ammonia is lethal for the fish. Fortunately there is a already a strong army in the aquarium to tackle this ammonia. The army is none other than the Beneficial bacterial colony.

The beneficial bacterial colony turns Ammonia into Nitrite and Nitrite into Nitrate. This is what the process looks like:

Ammonia -> Nitrite -> Nitrate

Nitrate is the end product. Now, nitrate is far less harmful than Ammonia. However, when nitrate starts to build up with time, it can slowly make the environment toxic for the fish. If no actions are taken, the nitrate will once get so high that it can kill the fish.

That’s why we perform regular water changes to keep the amount of Nitrate in check. When we fill in the tank with new & fresh water, it lowers down the amount of Nitrate, thus keeping the tank environment safe for all the fish.

So, Why Smaller Tanks Need Larger Water Change?

If the tank is smaller (let’s say less than 5 gallons), then the Nitrate will very quickly build up to the amount that is toxic for the fish. On the other hand, for a larger tank, it will take more time for the Nitrate to become toxic.

Let’s say within 1 week your tank produces 10 milligram nitrate (just an assumption).

Now, if your tank can hold 19 liter water (5 gallon), the concentration of nitrate after 1 week will be 0.5 milligram per liter (ppm).

On the other hand, if your tank can hold 38 liter water (10 gallon), the concentration will reduce down to 0.26 milligram nitrate per liter water (ppm).

As you can see, with the same growth rate of nitrate and after the same period of time, the concentration of nitrate can be much higher in a smaller tank compared to a larger tank.

That’s why it is recommended to do larger water changes in smaller tanks aka tanks that are smaller than 5 gallon.

Factors That Control The Frequency Of Water Change

There are many factors that can affect the frequency of water change in your tank. When you are determining how often to change water in a betta tank, you’ll need to consider all of these factors.

Is The Tank Cycled Or Not?

If the tank is not cycled, you’ll need to change water more often. Why? Because an uncycled tank doesn’t have an established beneficial bacterial colony. So, there is nothing to tackle the ammonia in the tank.

As a result, if you are not frequent with the water changes, the ammonia will soon build up and create a toxic environment for the betta.

As bettas are hardy, many people prefer not to cycle the tank before putting the betta. Though this is not recommended, it can work if you have a large tank (larger than 10 gallon) and only the betta living in it. It will be better if you also have real plants in the tank as plants can help to tackle the ammonia.

Now, I’ve already mentioned ammonia is dangerous for any water being. That’s why, until the tank is properly cycled, we’ll need to do more frequent water changes, preferably 15% everyday for the first 2 weeks.

Are There Other Tank Mates?

This is a very important yet simple concept to understand for every fish keeper. If an aquarium has lots of fish, then it will produce lots of bio load (meaning fish waste). Lots of bio load will in turn create lots of ammonia.

This is simply the equation:

Bio load from A 10 gallon tank with 5 fish < Bio load from a 10 gallon tank with 10 fish

So, the more fish you have, the more bio load they will create, as a result, the more frequent you’ll have to be with the water change. If you don’t want to make water change more than once per week, then you’ll have to perform a larger volume water change if the bio mass (number of living creatures in the aquarium) is heavy.

Is There A Proper Filtration?

Every aquarium needs to have proper filtration system. Many people keep betta in little bowls without any type of decent filtration. They think that bettas are hardy enough to live in a small bowl for the rest of its life.

This makes me extremely angry and frustrated. Suppose I have shoved you into a cupboard. I am giving you meals 2 times a day.

Now will you be alive after 1 month? Probably yes.

Will you be happy after staying in the cupboard for 1 month? DEFINITELY NO!

So, please don’t keep bettas in little bowls with no filtration. If there is no proper filtration, the tank will have no beneficial bacterial colony to tackle the growth of deadly ammonia.

As a result, you may need to change water daily or every other day (depending on the size of the tank) to keep the water relatively safe for the betta.

On the other hand, if you have a proper filtration, you’ll have an army of bacteria on your side to fight the deadly ammonia. So, in that case, you can push back the water change frequency to once a week.

Does The Tank Have Real Plants?

I have already mentioned why we do water changes. Remember about the nitrates? The beneficial bacterial colony eats Ammonia as food and eventually turns it into Nitrate.

Now, nitrate is a great food for plants. Plants absorb nitrate as fertilizer to grow. So, if you have real plants in the betta tank (which is recommended), then the plants will also help you to absorb Nitrate. In that case, you may push the water change frequency to once every 10 or 12 days depending on the amount of plants you have.

I have seen many betta fish keepers keeping their betta in a ‘no filter’ heavily planted tank for years. The betta stayed happy and thrived. The reason it worked because the plants worked as the filter and absorbed Nitrate.

Plants also produce oxygen, which of course creates a more comfortable environment in the tank for the betta.

Does The Tank Have Substrate?

If the tank has a good layer of substrate (sand, aqua soil, gravel, etc.), then it may need more frequent water changes than a bare bottom tank. It is because, the substrate helps to trap the uneaten foods, fish waste and all other organic matters.

These organic matters decay over time and give rise to ammonia. They also form gas pockets within the substrate which can be dangerous for the fish. This type of problem doesn’t occur in a bare bottom tank.

What Are You Feeding The Betta?

The food you are feeding your betta will also affect the water change frequency. If you are often feeding live foods like bloodworm, earth worm, daphnia, brine shrimp, etc., then these will quickly deteriorate the quality of the water.

In that case, you may need to do more frequent water changes in order to keep the water quality pristine.

Betta Fish Died After Water Change? Here’s Why

The most probable reasons for your betta fish dying after a water change are:

  • You haven’t treated the water with a water conditioner. If you are using tap water directly to the betta tank, then it can be deadly for the fish. Tap water contains chlorine and chloramine (in some areas) that are lethal for any fish. Before using them in the tank, we’ll need to treat the tap water with a good quality water conditioner (such as Seachem Prime). This water conditioner will remove the chlorine and chloramine, thus making the tap water safe for the betta.
  • The temperature of the new water is either too hot or too cold than the tank water. This type of rapid temperature change can put the betta into shock and kill it.
  • The parameters of the new water are way too off than the tank water. Though betta fish dying for this reason is very unlikely, it can happen if the parameters differ way too much from the tank water.

How Long Can A Betta Fish Go Without Water Change?

Betta fish can go for weeks without water change if the tank is large, has proper filtration and heavy plants. Also, the bio mass needs to be as low as possible (preferably only the betta).

However, that doesn’t mean we should actually neglect water change for weeks. Yes, your betta might survive if you don’t change water regularly, but that will be inhumane for the betta as it will live in a toxic environment.

Can You Use Tap Water To Refill The Betta Tank?

You can use tap water to refill the betta tank only after it is treated with a good water conditioner. Other wise, the tap water may contain chlorine and chloramine which will be deadly for any fish.

Why You Shouldn’t Change More Than 50% Water?

If you change too much water in one go, then several problems will arise:

  • As more than half of the tank will be refilled by new water, it can set off the parameters. This can have an impact on the beneficial bacterial colony and destroy it. If the beneficial bacterial colony gets destroyed, it will be a disaster for your betta tank. The tank will need to be cycled again.
  • If the parameters get set off too much, it can also have an adverse affect on the betta fish. As a result, the betta fish can go into shock. Sudden shock is not good for any fish.

So, this is all about how frequently you should change betta tank water. I hope you’ve found the guide helpful.

Happy betta keeping.

Muntaseer Rahman

I have been keeping shrimps as a pet for many years now. I’ve fallen in love with these cute pets from the moment I saw them. That’s why I am writing articles to share my shrimp keeping knowledge with you.

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