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How Often to Change Betta Fish Water: The Complete Guide

Water changes are basic maintenance for any fish keeper. No filter can process all of the waste that accumulates. And you’ll always need to add new water to replace that which evaporates over time. Bettas love it when you freshen up their tank but just how often do you change a betta’s water, anyway?

What Water Conditions Do Bettas Prefer?

Bettas are so incredibly popular because they can thrive in a wide range of water conditions. In the wilds of Thailand, they are found in shallow streams, rice paddies, ponds, and other slow moving, even stagnant bodies of water. In these steamy conditions, the dissolved oxygen content gets so low that other fish often can’t survive.

Fortunately, bettas have their labyrinth organ, which allows them to breathe air. See how your betta goes to the surface every few minutes to take a breath? It’s literally breathing air, just like us, because air holds around 100 times as much oxygen by volume as water does.

Besides preferring very warm conditions, bettas also prefer a soft, acidic chemistry. The weed-choked environment of their home is full of decaying plant matter. Plant tannins, humic acids, and other substances act as acid buffers, bringing the pH below 7.0. That said, bettas will thrive even in alkaline conditions; but if you can, keeping the pH below neutral will make them happier!

General hardness (GH) and carbonate hardness (KH) are also quite low. There are few dissolved minerals within the water, which is why their water is as soft as it is.

If you can, it’s a good idea to keep aquatic plants alongside your betta as well. Plants take in carbon dioxide (CO2) exhaled by your fish as a nutrient and release oxygen for them, improving the aeration of your tank. Plants also directly consume all three nitrogenous waste products (ammonia, nitrite, nitrate) and use it as food, making them beautiful little biological filtration systems.

And if your male betta is happy enough, he will likely try building a bubble nest. Plants that are growing near the surface are what he tends to look for because they act as anchors for his bubble nest raft. Once it’s secure and not at risk of floating away, he will likely start looking for a female betta to entice to his love nest.

Why are Water Changes Important?

Water changes are important because it’s the only way to remove certain waste products in your tank. And while some other chemicals will break down over time, they accumulate much faster than the breakdown processes occur, making water changes essential.

Water changes are like a spring cleaning for your aquarium. You open the windows, beat the rugs, dust the furniture…Together, the entire atmosphere of your home changes and you feel much better as a result. Your fish will grow lethargic as chemicals accumulate, making water changes are essential for proper health!

What Chemicals cause Bettas Problems?

The three major pollutants that should be part of any fish keeper’s vocabulary are ammonia, nitrite, and nitrate. Together, these chemicals form the backbone of the nitrogen cycle. In my article on biological filtration, I go into great detail on how this process works.

But to briefly explain, your aquarium, especially your filter, is home to beneficial bacteria that eat ammonia, the first and most toxic form of waste that fish and other organisms release. This ammonia gets digested and released as nitrite, which is less toxic but still a problem for most animals. Fortunately, a second set of bacteria eat that, converting it into nitrate.

Nitrate tends to then accumulate in your tank since the bacteria that eat nitrate need specialized conditions that are rare in most aquariums. Plants will also consume nitrate (as well as nitrite and ammonia) but unless you have a heavily planted Walstad tank, you can’t rely on them for all of your filtration needs. Therefore, we need to do water changes to remove this excess nitrate.

How Often to Change a Betta’s Water

There are a few factors that influence how often you should change your betta’s water. But the short version is that small water changes of 10-20% once every 7-10 days are best for your betta’s health. This is also assuming you are running a filter. You can also do water changes of 20-30% once every 2-3 weeks, but smaller water changes are better for stable water conditions!

How Often Do You Feed Your Betta?

How much food you give your betta is important – and not just because your betta needs to eat! Any leftover food will contribute directly to increases in ammonia and other waste products. So when fish guides say “never overfeed,” they mean two things: don’t allow any leftover food to accumulate without being eaten and don’t feed your betta too often!

Some aquarists believe that providing “extra food” is a good idea for their betta in case it gets hungry later. Any extra food is going to immediately start decaying and create problems for your fish. It’s better to underfeed than overfeed, in this case.

Bettas eat quite a bit in a single meal; one solid feeding per day is all that they require. They aren’t nearly as active as tetras and other fast-moving fish and don’t need loads of food. Feed your betta enough that it’s stomach rounds out visibly and it slows down. The more you feed your fish, the easier it will be to know exactly how much your betta will eat at every sitting.

If you enjoy interacting with your fish more often through food, you can also break up their meal into three smaller feedings per day. Like all fish, bettas are continually willing to eat since in nature, they never know when their next meal is going to come.

What Kind of Filter Do You Use?

If you purchased your betta with a Spider Vine or other plant growing out of its bowl, you may have been told that the vine “filters the water while the betta eats the vine,” in a sort of Circle of Life story. Sadly, this is entirely untrue.

The plant certainly does uptake ammonia and other waste products but not nearly enough to entirely purify a betta bowl. And bettas are 100% carnivorous; any root biting is due to the betta finding some small organisms to eat. Or it is exploring its environment with the only grasping tool it has: it’s mouth.

Whether you prefer a sponge, power, or canister filter, you should always use some kind of filter on your betta tank. Bettas have a reputation for not needing a filter because they are capable of surviving in small, stagnant bodies of water in nature.

But the key word here is survive. We don’t want our pets to simply survive in our care; we want to see our fish thriving, healthy and happy! So instead of providing the bare minimum, we can use a filter to process waste within the tank and lengthen the amount of time required between water changes!

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For the majority of aquariums, a high quality sponge filter provides plenty of filtration for a single adult betta plus some tank mates. Sponge filters provide not only loads of mechanical filtration capacity but also offer a home to beneficial bacteria that feed on ammonia, nitrite, and nitrate (biological filtration). Many sponge filters even have compartments for activated carbon (chemical filtration), completing the trifecta of ideal aquarium filtration!

Some betta tanks use undergravel filters but I’m not a huge fan of these. They trap waste under the gravel, where it tends to be slow to decay aerobically. And in order to clean it out, you must lift the plates, potentially filling the water column with dirt and disrupting your entire aquascape.

How Large is Your Betta Aquarium?

Contrary to popular belief, large aquariums are actually easier to maintain than smaller ones for one very good reason. The more water you have, the longer it takes for the chemistry to shift. Larger tanks keep within a stable temperature range, salinity, pH, and other parameters easily, which all fish prefer.

Still, you’re likely keeping your betta in a 3-5 gallon tank, which is still fine. It just means that you have less of an allowance for overfeeding and other potential pollution problems.

Changing Your Betta’s Water

While you can’t use untreated tap water, testing and treating it doesn’t take much time at all! A little modifying of the water’s chemistry will go a long way towards ensuring your betta remains healthy!

Supplies You’ll Need

  • Siphon Hose: a siphon hose is used to remove water from an aquarium into a bucket. Typically gravity powered, they can create a powerful amount of current that a long-finned male betta may not be able to resist. So keep an eye on the tank at all times when doing a water change!
  • Dechlorinator: untreated tap water typically has chlorine or chloramine in it. These chemicals are used as disinfectants to ensure bacteria aren’t transmitted into your drinking water. But these chemicals are toxic to fish and need to be neutralized before adding the water to your tank.
  • Water Test Kit: in order to monitor the conditions in your betta tank as well as the incoming tap water chemistry, you’ll need test kits for pH, GH, KH, and other parameters. Fortunately, you can get the majority of the tests you need in a single Freshwater Master Test Kit.
  • pH Adjusting Reagents: if your tap water chemistry is very different from the range you want to maintain in your betta tank, you’ll need chemicals to raise or lower to pH in order to keep in an ideal range. Bettas are hardy up to pH 8.0 but vastly prefer 6.0-7.0. They are much more likely to show better colors and breeding activity in soft, acidic conditions.
  • Bucket or No Spill Siphon Hose
  • Thermometer: when adding fresh water to the tank, a thermometer should be used to match the temperature as closely as possible. Temperature shocks can make fish sick just as with humans.
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When matching the temperature of your incoming fresh water to your betta’s aquarium, know that you don’t need to be super precise. You can add enough water to bring the temperature down 2-3 degrees from the usual temperature or raise it by 5 degrees with no issues. Shifts in heat are much better tolerated than cold for tropical fish. But I wouldn’t stress the fish by causing drastic shifts too far beyond these boundaries.

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In case you aren’t already, you should definitely have a heater for your betta as well. Once again, the toughness of bettas can make their lives more difficult than they need to be. While they can live in unheated water, they are Southeast Asian natives that prefer temperatures around 78-84℉ or even warmer.

Unheated room temperature water is around 65-72℉ and needlessly stressful for the poor fish. A simple plug-in heater sized for a small tank will boost their appetites and disease resistance in no time!

Water Change Frequency

For aquariums of all sizes, it’s much better to do frequent small (10-20%) water changes rather than infrequent large ones. Or rather, do both, but don’t rely on large (30%+ changes) infrequently.

The issue with large water changes is that they are a significant disruption to the established water chemistry. Bettas are extremely hardy and not likely to show too much stress. But it certainly won’t be thrilled with, say, a sudden pH shift of 6.5 to 7.5 after adding tons of fresh tap water. Other fish can be killed outright by such a change.


Water changes are important and very easy to do, so long as you follow a few essential steps first! Small, frequent water changes are always better than large, infrequent ones. When using a siphon hose, remember to watch out for your slow-swimming betta. And when adding fresh water, you’ll need to do your best to match the temperature and chemistry parameters because too quick of a shift can open up your fish to diseases and other problems.

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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