Can Cardinal Tetras Live In Hard Water?

Cardinal tetras are famous freshwater fishes that you can find commonly in any pet store. Moreover, due to these fish’ easy-going, peaceful, and schooling nature, they have become one of the favorites for both beginner aquarists and experienced hobbyists. However, a question lingers in the minds of many aquarium enthusiasts – can cardinal tetras live in hard water?

As Cardinal tetras adapt well in most environmental conditions, they can live in hard water. However, if the water hardness is too high, it can stress the fish and cause them to lose their color over time. To combat this, you can try to soften the water a little bit or keep the pH level of your tank slightly acidic.

The answer to this question is not as straightforward as it seems because it depends on many factors. This article will highlight the fact that cardinal tetra fish can live in hard water, but there are things to consider before you make up your mind about it.

What Is Hard Water?

Hard water is simply a type of water with high mineral content, making it difficult for salt to dissolve. It means that when you put food coloring in hard water, it will not color the entire cup because some of the dye remains undissolved. And it is due to its inability to penetrate the mineralized molecules present in the liquid.

Thus, soap scum forms in hard water areas – because the minerals (calcium and magnesium) bind with fatty acids from soaps to create a solid, scummy layer.

Can Cardinal Tetras Live In Hard Water?

The answer to this question isn’t simple since there are different types of hard water. Some forms of hard water have high calcium levels, while others have high magnesium levels. In general, though, Cardinal tetras can live in hard water as long as the water’s pH level is relatively neutral.

If you’re unsure about the hardness of your tap water, you can purchase a home water testing kit or take your water to a local pet store for analysis. If the water is too hard, you can soften it using a reverse osmosis system or an ion-exchange filter.

Cardinal Tetras are schooling fish and do best when kept in groups of six or more. If you decide to keep them in hard water, it might be advisable to add more fish than usual.

What Type Of Water Is Best For Cardinal Tetras?

Cardinal tetras are tropical fish, and as such, they thrive in warmer water. The ideal water temperature for Cardinal tetras is between 72 and 78 degrees Fahrenheit. Anything outside of that range could potentially be fatal to the fish.

Some of the primary water parameters needed for the healthy and longer life of Cardinal tetras are:


The water should be moderately hard or harder. While soft water does not cause any harm, it will significantly shorten the life span of your fish because they are more susceptible to diseases and infections in soft waters.

The ideal range is between 2 to 4 dGH, but anything within this range could work just fine.


The pH of the water should be in the neutral range, around a pH level of 4 to 6. Cardinal tetras can tolerate a slightly acidic or alkaline pH, but they will do best at a neutral pH.


As mentioned before, cardinal tetras thrive in warmer waters. Therefore, it would be best to keep them below 72 or above 78 degrees.


The level of ammonia should be 0 ppm (mg/l). Moreover, this is especially important if you are using an under gravel filter, as the gravel may release large amounts of ammonia into the water over time.


As with ammonia, nitrites levels should also be at 0 ppm.


The nitrate level in the water should be as low as possible. Below 20 ppm is ideal.

These are just some basic water parameters for keeping cardinal tetras healthy and happy. By following these guidelines, you can help ensure that your fish will have a long and healthy life.

Do Cardinal Tetras Need Water Changes?

Cardinal Tetras are freshwater fishes originating from the Amazon River basin in South America. So, they need clean and slight current water to thrive in the home aquarium.

Water changes are essential for keeping your tank clean and healthy, as well as providing a new source of oxygen for your fish. Therefore, you need to change the water in your tank at least once a week.

However, if your water is hard (alkaline), you may be able to get away with changing it less often. The harder water you have, the less often your need to change it.

It is because hard water tends to buffer against changes in pH that come from organic waste build-up or other sources of acidity. So when you do a partial tank replacement with very soft (and acidic) tap water, the buffering capacity of the hardness minerals in the water help to stabilize the pH and keep it from dropping too low.

How To Change Water In Cardinal Tetra’s Tank?

Cardinal Tetra Fish is one of the most common freshwater aquarium fish. However, they are also sensitive to water quality and, if not maintained properly, can lead to disease or even death. Therefore, you must monitor your Cardinal Tetras tank chemistry frequently for both ammonia and nitrite levels as well as pH levels throughout its life span.

The basic steps to change the water in Cardinal tetras’ tank are:

  • Turn off the heater
  • Drain all water from the tank using a siphon hose
  • Rinse substrate and ornamentation in hot tap water
  • Refill the tank with room-temperature dechlorinated water (or use a dechlorinator like Prime)
  • Add your fish back into their tank safely


What Happens When You Put Cardinal Tetras In Hard Water?

When you put Cardinal Tetras into hard water, they can often develop ich. This is because the parasite that causes it has a higher resistance to salt than most other fish parasites do. As such, if you have an outbreak of Ick while your tetra tank contains both soft and hard water fish together, you can expect that the hard water fish will get it first.

How To Treat My Cardinal Tetras For Ich?

The best way to treat for ich is by diluting your saltwater with fresh tap water and increasing the tank’s temperature. If you do not have a quarantine tank, this means netting all of your cardinal tetras out of the tank and treating them in a bucket or bowl. After treatment, you can then put them back into their original tank.

What Are The Problems When Your Cardinal Tetra’s Aquarium Contains Soft Water?

The biggest problem that you will run into when your cardinal tetras are in a soft water aquarium is that they can be more likely to contract ich. While this illness does not always kill them, it may cause you to lose some of your fish if treatment becomes necessary and no quarantine tank is available.

What Are Some Other Problems When Water Condition Changes In The Tank?

Cardinal tetras are very sensitive to changes in water chemistry. It means that if you have soft water, the pH of your tank can fluctuate fairly quickly and severely. There can be an increased risk of losing all or some of your fish if this happens.


Overall, the research showed that cardinal tetras could live in harder water. But they did not thrive as well as those living in softer water. There were lower numbers of cardinal tetras residing in the hard water tanks. They also exhibited lower levels of coloration. The stress of living in harder water may even contribute to the shorter lifespans of these fish.

Despite these findings, cardinal tetras can still live in hard water if you succeed in maintaining an ideal water condition. Therefore, if you want to keep cardinal tetras, it is vital to research the water hardness of your local area. It will help to ensure that they will thrive in your tank.

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