When it comes to setting up an aquarium, one of the most important considerations is the type of fish that will thrive in the environment. If you have hard water, it’s crucial to choose fish that are compatible with hard water. A hard water environment can support the thriving of many fish species. We have compiled a list of the top 10 hard water fish for 10 gallon tank that can comfortably live in conditions with high concentrations of minerals, particularly calcium, and magnesium.

What is Hard Water?

According to USGS Hard water is water that contains a high concentration of minerals, particularly calcium, and magnesium. If you have a liquid rock type of water with high water hardness, don’t worry. There are still plenty of fish species that can thrive and survive in such hard water environments.


If the dH (degree of hardness) of water measures between 0 to 6, and the ppm (parts per million) is within the range of 0 to 100, the water is classified as soft or very soft.

If the dH (degree of hardness) of water falls within the range of 6 to 25, and the ppm (parts per million) measurement is between 101 to 449, the water is considered to be slightly hard to hard.

If the dH (degree of hardness) of water exceeds 30, and the ppm (parts per million) measures 450 or more, the water is commonly referred to as “liquid rock” due to its very hard nature.

Factors to Consider

There are certain factors that you need to consider when choosing hard water fish for 10 gallon tank. These factors include:

Tank Size

While the minimum size for keeping fish in hard water is a 10-gallon tank, it’s important to note that a larger tank will provide a more comfortable environment for your fish to live in.

Water parameters

Choosing the right fish for your hard water 10 gallon fish tank requires consideration of various factors such as pH, temperature, and water hardness. Since different fish have different requirements, it’s important to select fish that can thrive in the specific conditions provided by your hard water.

Behavior and compatibility

Compatibility is a crucial factor to consider when selecting fish for your tank, as some fish tend to be more aggressive than others and may not get along well with certain species. Therefore, it’s important to choose fish that are compatible with each other and won’t harm one another.

Best Hard Water Fish for 10 Gallon Tank

Having covered the essential factors to consider, let’s now delve into the top 10 hard water fish that are suitable for a 10-gallon tank.

Related Post: 7 Best Fish For 36 Gallon Tank

1. Guppies

Guppy Fish
Image source:Wikimedia commons

Guppies are a well-known favorite among beginner fish keepers, and they’re also compatible with hard water environments. Their vast array of colors makes them an attractive addition to your tank, and they’re relatively low maintenance.

Guppy water’s pH requirement falls between 7.0 and 8.2, with an optimal water hardness range of 20 dgH. For a balanced diet, a combination of flakes and live food is essential. A 10 gallon tank can comfortably accommodate up to 5 guppies.

2. Endler’s Livebearers

Endler's Livebearers
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Endler’s Livebearers are similar to guppies but are smaller in size. These are gorgeous beautiful fish that are also highly adaptable and can thrive in a range of water conditions, including hard water.

Endler’s Livebearers with a pH between 7.0 and 8.2 and water hardness between 10 to 30 dgH. They also need a varied diet that includes both flakes and live food. You can keep up to 6 Endler’s Livebearers comfortably in a tank of 10 gallon.

3. Congo Tetra

Congo Tetra: Hard Water Fish for 10 Gallon Tank
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Congo Tetras are comparatively long and flat, with a towering midsection giving them a compacted look. Males are often a little bit bigger than females, but females have a plumper appearance, especially when they are ready to procreate. Congo Tetra originated from the Congo River basin in Africa.

Congo Tetras are known for their hardiness and ability to thrive in hard water environments, making them a great addition to any 10-gallon aquarium with such conditions. They can easily tolerate a pH range of 6.0 to 8.0 and dgH between 5 to 25.

4. Molly

Orange Molly fish
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Molly fish is another type of livebearer that require hard, alkaline water to thrive. These fish are often bred in fish farms that utilize brackish water, similar to the conditions in which guppies are typically raised. So Molly Fish can be the best hard water fish for 10 gallon tank. Mollies are capable of living in a pH range of 7.5 to 8.5, and they require a water hardness level of 12 to 30 dGH to survive in a hard water environment.

One potential problem with keeping Molly fish in a 10 gallon tank is that they can outgrow the space as they grow quite large, reaching sizes between 5 and 13 cm. If they become too big for the tank, you may need to consider upgrading to a larger tank.

5. Flagfish

Flagfish: Hard Water Fish for 10 Gallon Tank
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The American flagfish is a fish specie with a distinctive appearance that closely resembles the design of the American flag, which is how it earned its name. This fish species is capable of growing between 5 to 5.5 centimeters in size. The general hardness (gH) level of 9-20 dGH is generally considered to be within the survival range for Flagfish.

If properly cared for, the American flagfish can be an excellent choice for a 10-gallon tank and can make a wonderful pet.

To choose the best fish for your hard water 10-gallon tank, it’s essential to carefully these several factors. By selecting fish that can adapt and thrive in the specific conditions provided by your hard water, and ensuring that they are compatible with each other, you can create a healthy aquatic community in your tank.