Is Distilled Water Safe For Fish? (Why Not + How To Make It Safe?)

Image of a woman holding distilled water

The quality of water in a fish tank greatly affects the health and well-being of its inhabitants. Distilled water is free from contaminants and dissolved solids. Since fish need clean and hygienic water to thrive, it may seem like a good choice for aquariums. However, is distilled water safe for fish?

Distilled water is not safe for fish as it lacks the useful minerals needed by fish and aquatic plants. You can use distilled water for topping up an aquarium or for reducing the water hardness. However, pure distilled water is not a good choice for aquariums as it is prone to wide pH fluctuations.

Let’s take a closer look at this now.

Why Is Distilled Water Not Safe For Fish?

Through distillation, we purify water. Distilled water does not contain trace minerals like calcium and iron, which fish need to stay healthy. Hence it is not suitable for them.

Another factor to remember is that the minerals in water play an important role in maintaining pH levels. These minerals act as buffers. Since distilled water is devoid of these minerals, it is highly prone to pH fluctuations.

Each type of fish needs a specific pH range to survive. Although they will tolerate slight changes in water chemistry, significant variations will affect their health. It can even cause death. Unfortunately, distilled water is prone to high pH variations.

Fish also need the ions in dissolved salts for their neurological activities. These ions help them transmit nervous signals.

In the absence of such ions, the fish can suffer neurological inabilities. Hence, it is unsuitable for most aquatic organisms.

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A Close Look At Distilled Water And Its Properties

Distillation is the process of boiling water till it evaporates and then cooling it back to liquid form. When water evaporates, the solids in it are left behind. The resulting liquid is pure as it does not have any dissolved solids. The water after distillation is one of the purest forms of water.

Given below is a diagram showing the water distillation process in a laboratory.

Water Distillation Process
Water Distillation Process

Unlike tap water, distilled water is free of contaminants. It does not have any harmful parasites, heavy metal ions, organic impurities, or pollutants. Hence, it may seem like a good and clean choice for your aquarium. However, distillation also strips the water of essential minerals and ions.

Beneficial minerals like iron, calcium, and magnesium are also left behind after distillation. However, aquatic animals and plants need these minerals for their health. These elements help to maintain a constant water pH. But, distillation strips the water of these useful nutrients.

Distilled water in its pure form has a pH of 7, which is acidic. But this pH is not constant because pure water tends to absorb carbon dioxide and other gases.

When distilled water absorbs carbon dioxide from the surroundings, its pH level changes. Hence, it is highly unstable.

Is Distilled Water Good For Freshwater Fish Tanks?

You should not use distilled water to fill your freshwater aquarium. This water lacks the minerals and ions needed by freshwater fish for their health. Distilled water is also extremely soft and prone to wide pH fluctuations. It can prove deadly for your freshwater fish since they need a consistent pH for survival.

However, you can use distilled water to top up your aquarium.

You can also add minerals to pure distilled water based on the needs of your aquatic animals and plants. The minerals will also stabilize the water. Hence, you can add it to your fish tank.

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Can You Use Distilled Water In A Saltwater Fish Tank?

The water parameters in a saltwater fish tank, like pH, hardness, and salinity, should be more precise than in freshwater tanks. The slightest changes can introduce algae and affect the health of the inmates of the tank.

Marine fish and creatures belong to environments with minerals and salts like calcium, iron, and magnesium. These minerals play an important in supporting their biological systems. Distilled water lacks these minerals and ions. Hence, it is not a good idea to use distilled water in a saltwater fish tank.

Filling your saltwater aquarium with distilled water will adversely affect your marine fish and plants. Apart from the lack of minerals, they will also find it difficult to adjust to the pH variations of the tank.

However, you can use distilled water to top up your saltwater aquarium. You can add suitable quantities of salt to the water before adding it to the tank. You can also use distilled water for pH level adjustments.

Is Distilled Water Ok For Tropical Fish?

Tropical fish need temperatures between 24°C and 27°C and pH levels between 5.5 and 7.5 to survive. Depending on the species, it will need a smaller temperature and pH level in this range.

Freshly distilled water has a pH of 7, which falls within this range. Hence, it may seem suitable for tropical fish.

However, distilled water will not maintain this pH level for a long time. It is prone to wide fluctuations. The pH of distilled water can fall to levels as low as 5.8 in a few hours.

This wide fluctuation can drastically affect their health and kill tropical fish. The absence of minerals and ions in the water will also affect their well-being. Hence, distilled water is not a good choice for tropical fish tanks.

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How To Make Distilled Water Safe For Fish?

Fish enjoy a better quality of life in natural or freshwater that contains essential minerals. Hence, distilled water in its pure form is unsuitable for fish tanks. You should not use it to fill a fish tank or for water changes.

However, you can use it in limited quantities for the following needs:

  • To top up a fish tank: You can use distilled water to compensate for water lost from the tank through evaporation. The lack of minerals in it will not affect your fish since the existing tank water will have these essential minerals.
  • Adjust the hardness of water: If your tap water is hard, you may have to soften it before adding it to your tank. In this case, you can use distilled water to reduce the water hardness. Mixing suitable quantities of distilled water with your tap water will reduce water hardness and stabilize the pH.

If you wish to make distilled water safe for fish, you can do so by adding the missing essential minerals into it. Fish need minerals like calcium, magnesium, and iron in trace quantities for their health and well-being. Since distilled water lacks these minerals, you should perform remineralization before adding it to your fish tank.

The benefit of using this approach is that the water for the tank will be pure. Since distilled water has a very low TDS or Total dissolved solids level, it will be pure and free of harmful pollutants.

To add the essential minerals to the water, you can use a salt mix. You will not have to worry about the presence of any harmful heavy metals or other toxins in the water. Hence, re-mineralized distilled water is one of the best choices for any aquarium.

Nevertheless, check the pH level before adding re-mineralized water to your aquarium. Also, continue to monitor the pH levels consistently to ensure that the water is stable and safe for your pets.