Should Aquarium Water Be Hard Or Soft? (Alter Water Hardness)

Image of a fish swimming in aquarium water

Water quality impacts the health of fish, aquatic plants, and other creatures in an aquarium. Hence, fish tank owners should have a basic understanding of water chemistry to keep the water parameters of their tank under control. When setting up an aquatic habitat, water hardness has great significance. So, should aquarium water be hard or soft?

Whether aquarium water should be hard or soft depends on the type of fish and aquatic plants in the aquarium. Most freshwater fish thrive in moderately hard or soft water. However, certain tropical fish can survive only in soft water. Moreover, some fish will successfully breed only in soft water.

Hence, the preferred hardness level basically depends on what your aquatic life needs. While some species of fish need hard water, others need soft water. To understand this better, we should explore what “hardness of water” means and why it is important in aquatic habitats.

What Is Water Hardness And Why Is It Important For Aquariums?

If you are a fish hobbyist, you must be familiar with the term “pH.” You may also know that maintaining a constant pH is important for the well-being of fish and other aquatic creatures.

The term pH describes how acidic or alkaline a solution is. In this case, it is the water in your aquarium. Water hardness is linked to pH. Hence, it is an important factor for aquariums. Hard water usually has a high pH, while soft water has a lower pH level. By adjusting the softness or hardness of water, you can better moderate the pH levels of your aquarium.

When your fish live in water at the right pH level, they will be healthy and lead long lives.

The hardness or softness of water depends on the minerals dissolved in it. Hard water has a higher mineral content than soft water. Rainwater and water in lakes and ponds are usually soft. Meanwhile, the water in wells and rivers is hard due to the presence of minerals.

The hardness of water is usually described by two terms:

  1. General Hardness: General hardness or GH is a measure of the magnesium and calcium level of water.
  2. Carbonate Hardness: Carbonate hardness or KH measures carbonate and bicarbonate ions in water.

So, the presence of magnesium, calcium, carbonate, and bicarbonate ions in the water makes it hard.

When there are minerals in the water, it is less prone to pH fluctuations. Hence, hard water shows fewer pH changes and is a more stable environment for your fish. With appropriate water hardness, it will be easier to fix pH levels and maintain the consistency of water in a fish tank.

Now, the question is, how hard should aquarium water be? Let us find out.

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How Hard Should Aquarium Water Be?

In most places, tap water is hard water. It has plenty of mineral ions that are good for your fish.

When you use tap water in an aquarium, pay attention to the GH or general hardness of the water. It will help you decide whether the water is suitable for your plants and pets.

The recommended degree of general hardness will depend on the type of fish you have. A 4 to 12 dGH is usually suitable for most tropical fish and shrimp tanks. For a planted tank, the ideal dGH range is 3 to 8.

The best way to determine the general hardness of your fish tank is with a testing kit. These kits are usually available at pet stores. You do not have to test the water too often. Just check the GH every time you do a water change using a testing kit. It will indicate whether your pets and plants have optimal living conditions.

Is Soft Water Good For Aquariums?

Soft water does not have minerals like magnesium, calcium, or carbonates. These minerals play a crucial role in maintaining a stable pH.

Water in an aquarium tends to become acidic over time. However, when you use soft water in an aquarium, it is more prone to pH changes. Hence, it will become acidic must faster. Such rapid changes in pH will adversely affect aquatic life and cause stress to them.

Another additional concern is that the good bacteria that perform filtration in aquariums prefer hard water. Their cleaning activity is less pronounced in soft water. Hence your natural filters will not be enough.

Due to the above reasons, soft water is generally not preferred in freshwater aquariums. Nonetheless, you will need soft water in the following situations:

  1. Some fish, like tetras and South American dwarf cichlids, survive in hard water. However, they will only breed in soft water. If you are looking to breed these types of fish, you will have to keep them in soft water.
  2. Delicate fish, like Discus and certain Rasboras, cannot adapt to hard water. In such cases, a soft water aquarium becomes necessary.

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Do Aquarium Plants Like Hard Or Soft Water?

Aquariums are often home to not only fish but also live plants. In such arrangements, you should look at the water chemistry needs of the plants as well.

Most common aquarium plants thrive in hard water. In general, the preferred carbonate hardness for plants is about 3 to 10 dCH. The bicarbonates in hard water may even boost the growth of plants like Vallisneria.

How To Alter The Water Hardness In An Aquarium?

Once you understand the basics of water chemistry, it is easier to change the hardness to the level you need. You can achieve the desired hardness by adding agents that will successfully change the hardness levels. Let us explore this in closer detail.

How To Reduce Water Hardness In Aquariums? (How To Lower pH In Fish Tanks?)

You can use a reverse osmosis filter or ion exchange resin to soften aquarium water. These devices remove salts, minerals, and other ions from the water even as they purify it.

You can also use peat moss for the purpose. Place it in a mesh bag inside your filter. It will trap minerals in the water. Driftwood also works in the same way.

How To Increase Water Hardness In Aquarium?

If the water in your aquarium is too soft, there are a few ways in which you can increase its hardness.

Crushed coral, shells, and oyster shells will add carbonate ions to the water and increase its hardness. You can also use limestone or buffer additives.

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Should Aquarium Water Be Crystal Clear?

A well-maintained aquarium will have clear and healthy-looking water. Colorless and clean water is generally an optimal living environment for the inmates of a tank.

However, aquarium water will become cloudy or discolored over time. The water tends to become dirty because of food waste, fish excretions, algae, and other multiple factors. Dead and decaying plant or animal matter can also affect the clarity and quality of aquarium water.

Dirty water adversely affects the health of fish and aquatic plants. So, it is important to keep your tank clean. Invest in a good filtration system to keep the water clean all the time. Change the water regularly and perform timely maintenance. Clean the filters and substrate in the aquarium to remove any dirt, debris, or decaying matter. It will enable you to maintain water hygiene and make your tank a better living space for your pets.