Some fish have different water quality needs. One of the ways fish can vary from species to species is the amount of hardness they need in their water. Hardness refers to the amount of calcium and magnesium that is concentrated in the water. Before buying fish for your aquarium, research the hardness in the water in your area. A hardness of 9 – 30 is considered hard water. Here are some of the fish that do best in a hard water environment.
Marbled Hatchetfish are a unique hatchet-shaped fish that do best in hard water, while they will tolerate soft. They are a top feeder, as they have mouths located on the top of their bodies, and do well in a community tank. However, they do require some live food to survive, and enjoy being in groups of five or more.
Discus are a popular fish that many people choose to keep in aquariums by themselves in larger specialized groups. These fish enjoy slightly hard water. They come in a wide range of colors, from stunning teal to orange. They do need a large aquarium, as they grow quite large in captivity. They are a peaceful fish and make quite a distinguished addition to an aquarium.
Oscars also prefer slightly hard water. These fish have a reputation for being slightly aggressive, but if they are kept in groups of around six, they do just fine. Keep in mind that they also grow quite large and need plenty of breathing room.
Bettas do extremely well in hard water. In fact, they can tolerate hardness as high as 35 degrees! If you have hard water, be sure to include one male beta in your tank, as they will add a nice bit of color. Do not include more than one betta, though, because they will fight each other. They do fine with fish of other species.
Paradise fish are a hard water loving fish. They can tolerate a hardness of thirty. These colorful fish are slightly less aggressive towards each other than bettas, but do better if they are the only one of their kind in the tank. They have a very beautiful teal and red coloring, with flowing fins.
Live bearing fish, such as swordtails, enjoy hard and slightly alkaline water. These fish are a lot of fun to keep, as you will be able to breed them quite easily. Make sure to keep several females in the group, even though the males are the ones with the interesting sword fin. Mollies are another live bearing fish that absolutely must live in hard water. They can tolerate extremely hard conditions, and like to have a little salt in their water. Also, add the popular guppy to the list of hard water live bearing fish. They will tolerate slightly soft water, but to truly thrive they need hard water.
Finally, gouramis are a fish that like to be in hard water, while they will tolerate some soft water. Gouramis are interesting because of their unique long slender “feelers” that they have on the front of their bodies. These fish are very elegant looking when added to the aquarium.