Can Distilled Water Be Used in a Saltwater Aquarium?

-- By Carol

Setting up a marine aquarium can be a fascinating and rewarding experience but you should be familiar with the processes and equipment involved.

The most basic ingredient to any aquarium is water. Yet, choosing the right water quality can be confusing for first-timers.

Some people fail to even give this a thought and end up using tap water for their aquariums, which is a bad move.

Water supplies in most cities contain toxic chemicals such as chlorine, fluoride, phosphate, copper, chloramines, and nitrate that are harmful to fish and invertebrates.

While it’s possible to remove chloramine and chlorine using chemicals, you can’t do anything about other toxins that will continue to build up in your aquarium over time that increases the hardness of the tap water.

Distilled water is a better option, but is it recommended?

Let’s find out what exactly is distilled water.

Table of Contents

What Is Distilled Water?

Distilled water is the type of water that has gone through the process of distillation.

This involves heating the water to boil it and then cooling it to condense it back to the liquid state.

This process not only kills bacteria but purifies the water from sodium, gases and other contaminants that are left behind at the time of evaporation.

The resultant water is solely composed of hydrogen and oxygen molecules and has a pH level of 7.

Since all the minerals have been removed from it, distilled water has a blander taste.

It is certainly one of the purest water types and is available at most grocery stores. However, despite its purity, distilled water is not free from contaminants.

Even though the distillation of water guarantees 0 total dissolved solids (TDS), some volatile solvents and organic compounds with a low-boiling point that water might also evaporate with hydrogen and oxygen molecules.

This means that the distilled water will need more filtration to remove such pollutants.

We’ll discuss in detail whether they’re ideal for use in saltwater aquariums but the fact that it is expensive and impractical for larger tanks makes them unfeasible for many aquarists.

What Makes Distilled Water Unsuitable for Aquariums?

You must be thinking that distilled water is pure and thus safer for marine life. But that’s not the case.

The problem with distilled water is that it is too pure for marine life. It turns out that fish need more than hydrogen and oxygen to molecules to survive. Their natural habitat such as oceans, lakes, rivers, streams, and other water bodies comprise of minerals, such as calcium, iron, and magnesium that support the biological systems of marine life. Thus, fish thrive well in aquariums with fresh or natural water that hasn’t been stripped of all the minerals.

Besides the minerals, the process of distillation also affects the aquarium’s pH stability and other factors associated with the survival of fish.

This means that you should avoid using distilled water, particularly when you’re changing the water in your saltwater aquarium.

Distilled water typically carries a pH level of 7, which is considered slightly acidic.

Filling your aquarium with distilled water all of a sudden will cause an abrupt change in the pH level and other mineral content can prove fatal for your fish.

When it comes to pH levels, you need to understand that maintaining a stable pH level is important.

Fish can adapt to gradual changes in pH, but fluctuating levels can be detrimental for them.

Another reason why you shouldn’t solely use distilled water in your saltwater aquarium is that it affects your fish’s neural health.

Fish need ions or charged particles present in salts for transmitting signals through their nervous system.

Keeping them in pure distilled water means that the salts present in their bloodstream and other parts of the body will quickly dissolve, severely damaging their nervous system.

Unfortunately, no fish species is immune to this impact.

There can also be issues with the distillation process itself as you aren’t sure what materials are used in the equipment used for distillation.

Some distilleries use copper kettles and pipes, lacing the water with copper, which is highly toxic to marine life.

Oftentimes, large quantities of distilled water are produced and stored in metal tanks and delivered via metal pipes.

So the water might contain high levels of metals that are highly toxic to aquatic life.

On top of that, distilled water is also reported to be treated with antibiotics and algicides.

Due to this osmotic stress, some freshwater invertebrates are harmed by prolonged exposure to pure distilled water.

Another reason why distilled water is not preferred by most aquarists is that it is expensive and makes tank maintenance inefficient.

When Can It Be Used Instead of Distilled Water in Aquariums?

However, this doesn’t entirely rule out distilled water use in saltwater aquariums. By adopting some techniques, you can safely use them.

Here are some of the right ways to use distilled water:

Remineralizing Distilled Water

The best way to use distilled water is to mix it with minerals.

This remineralized distilled water makes among the top choices for saltwater aquariums because it is no longer harmful to your fish.

Not only will your aquarium be pollution-free but also include the minerals essential for your fish’s very survival. But how do you remineralize the distilled water?

How to Remineralize Distilled Water?

If you wish to carry out the process by yourself, you might simply want to add calcium chloride, baking soda, and Epsom salt to the distilled water.

As an easier and safer option, it is recommended to opt for a commercially available product.

If you have a planted tank, try Seachem Equilibrium as it doesn’t contain phosphates.

Seachem Replenish is a viable option for unplanted tanks. You should also add a salt mix to your saltwater aquarium.

Maintaining the Right Mineral Balance

On the other end of the spectrum, too much water evaporation in your aquarium can make the water acidic, which is again harmful to your fish.

The lost volume of water can significantly increase the proportion of mineral content present in your aquarium, making them much higher than the water molecules.

To avoid this, add some distilled water to your saltwater aquarium to compensate for the water lost through evaporation.

Reducing the Hardness of Tap Water

As mentioned earlier, the hardness of tap water doesn’t favor your fish.

Distilled water incredibly reduces the hardness of tap water to almost half its initial value.

Mixing a gallon of distilled water with a gallon of tap water with a general hardness (GH) of 20 will result in water with 10 GH.

A common misconception here is that the pH level of the resultant water will also be halved. That’s not true.

Whether the pH level will drop essentially depends on alkalinity or the carbon hardness (KH) of the water.

With KH levels of 2.5 to 3, no serious fluctuations will occur in pH levels, which may even remain the same.

Hence, you can safely dilute tap water with 3 KH with distilled water to reduce the hardness by half, without fearing a reduction in the pH level.

The Best Water Type for Your Aquarium

The best option for your saltwater aquarium is Reverse Osmosis and Deionized water (RO/DI).

Reverse osmosis removes 90 to 99% of the impurities present in water filtering it using a semi-permeable membrane and other filters.

Compared to distillation, this process is inexpensive. De-ionizing water helps to completely remove anions like nitrates and chlorides.

The major reason why this RO/DI water is preferred over distilled water is the problems associated with the distillation process in production plants.

The metal elements, such as copper from pipes can penetrate the water posing serious threats to marine life.

That’s the reason why most companies won’t state how they distill the water.

Distilling the water on your own can solve the problem but that is a costly solution.

Buying a reliable RO/DI water filtration unit is a much smarter idea that typically costs around $200.

Not only will you be tension-free about the metal penetration issue, but also avail an added advantage of limited algae growth in your tank, which is achieved due to low phosphate levels.

The only limitation of RO/DI water is that like distilled water, it also requires remineralization.

Key Takeaways

Based on the discussion above, it follows that pure distilled water can lead to dramatic changes in the body systems of your fish.

Like humans, fish are sensitive to any significant changes in the surrounding environment.

Not only are abrupt pH alterations dangerous, but certain minerals either favor or threaten the fish’s survival.

While certain circumstances such as water evaporation and tap water use require distilled water, aquarists need to adopt certain protocols to ensure fish safety.

The most important measures include not using distilled water only, remineralizing distilled water before use, and mixing it with tap water.

However, the copper penetration issue with the distillation process is still a question mark for using distilled water.

Thus, a more viable solution is to use remineralized RO/DI.

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