Best Aquarium Fish for Hard Alkaline Water

By Eddie Waithaka @aquariawise

Best Aquarium Fish for Hard Alkaline Water

Many hobby fishkeepers are not privy to this, but hard water limits the fish you can host in your aquarium.

While many tropical species will thrive without much hassle, some like discus and angelfish won’t flourish in anything other than soft water.

From experience, the best fish to keep in a hard water aquarium are African cichlids (mbuna, peacock cichlids, haps) and livebearers (mollies, platies, swordtails, guppies).

Some central American cichlids will thrive as well, same as synodontis catfish, barbs, rainbow fish, and even goldfish.

Many cichlids love hard water, but not all. Remember, even discus and angelfish are cichlids too, same as red Oscars, all of which thrive in very soft water that rests at a neutral ph.

In context, hard water is water with elevated dissolved levels of minerals, more so calcium and magnesium, and is notorious for leaving crusty scale build-up on aquarium glass surfaces.

Please note that the degree of hardness referred to by most aquarists while speaking of hard water is general hardness (GH) and not carbonate hardness, though KH (carbonate hardness) is also crucial because it functions as a buffer to your aquarium ph.

Carbonate hardness is the measurement of carbonates and bicarbonate present in your water. The total alkalinity of your fish tank will be high if your water has a high carbonate level, which also means it’ll be more basic (high ph).

Because of the mineral content in most hard water sources, chances are your hard water will also have high alkalinity (more basic).

In general, most fish will either favor a softer-acidic environment or harder-more-alkaline water depending on their actual wild environment. African cichlids do best in water as high as 20dGH (over 30ppm).

See more insight below.

What Fish Do Well in Hard Water

As discussed above briefly, different fishes prefer varying water hardness parameters, mostly showing preference to the settings closest to their wild environment.

Even so, some species are hardy and will survive in a wide range of water conditions regardless of how hard the water in their wild environment is.

Based on experience, below are the fish families I would recommend keeping in your aquarium if you only have access to hard water.

African Rift Lake Cichlids

Priced for their brilliant colors and infinite shades, African cichlids are also notable for their affinity for hard water, which is akin to their wild environment in the great lakes of Eastern Africa: Malawi, Tanganyika, and Victoria.

Lake Malawi water is overall alkaline with a ph of 8.5, a general hardness around 7, and a carbonate hardness of 10 to 12.

The water in Lake Tanganyika is medium hard with a GH from 7 to 11 and a ph varying from 7.8 to 8.8. Lake Victoria has almost similar readings.

As such, almost all species of fish from these lakes will thrive in a hard water aquarium, including all cichlids species and some bottom-dwelling catfish like synodontis.

The most commonly kept of these African cichlids are Mbuna, Peacocks, and Haps from Lake Malawi. Lake Tanganyika cichlids including Julidochromis, Lyretail cichlids are also common.

With all the buzz about marines, keeping the stunning African cichlids is like having a marine tank without all the hassle involved with saltwater


Livebearers is a group of popular aquarium fish that give birth to live young ones.

The most common of all are guppies, though mollies, platies, and swordtails are not strangers to the hobby either.

Many livebearers species come from Central and South America, and all do exceptionally well in hard water. Mollies even appreciate salt in their tank, while guppies can survive in an environment with a salinity level of 150 percent than normal seawater.

Please note that while salinity is not synonymous with hard water per se, saltwater is more often than not moderately to very hard.

That said, please note that not all livebearers can tolerate the same level of water hardness. Below is a brief look into each of the four (mollies, platies, guppies, swordtails) most commonly kept species.

Mollies in Hard Water

Mollies naturally occur in hard water and should be maintained in the water of the same quality.

They have evolved to function in such environments and have adapted over time to depend on the minerals in hard water (primarily calcium and magnesium) to thrive.

Of all livebearers, mollies are probably the only species that will not thrive in soft water, meaning you might want to remineralize water from your soft-sources.

Mollies originate from water-ways with high mineral content and ph levels, and while most tank-bred fish adapt to a wide variety of conditions, mollies are a bit of an exception. They really can’t thrive in soft water.

Guppies in Hard Water

Like most livebearers, guppies enjoy a ph level of 7.0 or greater. They also like hard water with sufficient amounts of calcium, magnesium, and other essential minerals.

However, unlike mollies, guppies tend to be more adaptable to mildly hard water. But it’s best if your water is naturally soft to add minerals to provide the best environment for your guppies.

Platys in Hard Water

The ideal water hardness for platys is anywhere between 10 and 28dGH and an alkaline ph from 6.8 to 8.0.

However, platys are quite adaptable and can tolerate a wide range of water conditions, but avoid sudden changes in parameters as this can lead to stress.

Please note that water filtration is also very crucial when keeping platys, more so when you have swordtail platys as they are more vulnerable to bad water conditions than other variations.

Swordtails in Hard Water

Same as platys, swordtail fish are sturdy tropical species that can tolerate a wide range of water conditions. But the ideal setting is hard water anywhere from 12 to 30 dGH and a ph between 7.0 and 8.4.

Plus ensure your water is properly filtered.


Cyprinids are a large group of tropical fish that include carps (discussed separately a little later) and minnows and their relatives, such as barbs.

Mnay cyprinids make great fish for the beginning aquarist because they are easy to care for and undemanding. They do well in most water conditions, though some do better in soft, slightly acidic water.

From experience, the best species from this family to keep in hard water are minnows, barbs, danios, and rasboras.

Minnows in Hard Water

A perfect fish for beginner aquarists, white cloud minnows are peaceful and undemanding. They are very forgiving with regard to water quality and temperature, plus they’ll feed on standard flake and pellet foods.

Though white clouds will live in a heated aquarium, they are usually more active and healthier at a temperature lower than those at which tropical fish live.

Water hardness can be anywhere from 5 to 19 dGH and ph levels between 6.0 and 8.0, meaning your fish will live in your hard water tank without much hassle.

Barbs in Hard Water

An active schooling species, tiger barbs grow to two inches and need a spacious tank for swimming.

The fish, though pretty adaptable, have a reputation as fin nippers and should not be kept with slow-moving fish with long fins such as gouramis, including betta.

Tiger barbs do well in a ph of 6.5 to 7.8 and moderately soft to relatively hard water.

These fish will survive in water with a general hardness anywhere from 2 to 30 dGH. You only need to make sure you have them in a school of six to seven individuals to bring out their social side and help tame aggression.

Danios in Hard Water

Danios are a popular schooling fish of the cyprinid family. They are incredibly hardy and can tolerate a wide range of water chemistry, making them an excellent choice for beginners.

Like white cloud minnows and goldfish, you can maintain danios in unheated tanks since they prefer things on the cooler side.

A ph anywhere is from 6 to 8 is ideal for danios, though they do best in 6.5 to 7.5. To keep them as hearty and active as they should be, use soft to moderately hard water in your fish tank.

In general, your danios should be able to live in water with a hardness anywhere from 5 to 19 dGH.

Synodontis Catfish

Synodontis catfish, also known as pygmy leopard catfish, grows to a length of approximately 4 inches and are native to African Great lakes (Tanganyika, Victoria).

As such, they are used to the relatively hard water and alkaline ph, a lot like African cichlids that are native to the same region.

These adorable finnies are renowned for their peaceful and inquisitive nature and benefit from stimulating decor.

They do best in a Lake Tanganyika biotope setup, with plenty of open waters for swimming. Add rocks arrangement in their tank for exploration.

Same to other catfishes, they appreciate and are more sociable in dim aquariums akin to waters at the bottom of the lake where they dwell.


Most loaches kept in home aquariums are not demanding in terms of ph and hardiness. They will tolerate a setting anywhere between 6.5 and 8 and moderately hard water.

Weather, dwarf, and clown loaches do best with a neutral ph and in medium-hard water, but they are also pretty adaptable, and slight variances won’t hurt them.

Their physiology is designed to handle occasional variations. You only need to make sure they are not extreme.

Loaches that have evolved to live in certain conditions over time, such as those bred at home, are also more likely to withstand higher water alkalinity and hardness than wild-caught individuals.

Given their adaptability, these loaches some of the very few fish species that can be maintained with African cichlids with minimal challenge.

Central American Cichlids

Central American cichlids are another group of adaptable finnies that do well across a range of water chemistry. As such, there are very few easy to obtain CA cichlids that you’ll have to worry about if you only have hard water.

A more pressing concern would be keeping your water clean with frequent changes because most CAs come from fast-flowing streams and rivers with pristine water and are sensitive to poor aquarium water quality and low oxygen.

Central American cichlids prefer a ph of 7 to 8 and a hardness of 10 degrees dh or more. Meaning in soft water areas, some hardening of the water may be necessary.

Thats all; Enjoy keeping fish🐠🐟🐡.

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