Can I Use Distilled Water in My Fish Tank? What You Need to Know

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Can I use distilled water in my fish tank?

If you’ve just started maintaining an aquarium, you’ve probably asked yourself the same thing.

After all, it simply makes sense to use clean, safe water for the fish you plan to take care of, right?

The truth is, distilled water isn’t as suitable for fish as you might think.

Fish need much more than water molecules; they need the minerals and dissolved solids absent in distilled water.

So, is there any way you can use distilled water in your fish tank? If not, what else can you use?

Can I Use Distilled Water in My Fish Tank?

If you’re planning to use distilled water to change the water in your fish tank, you might want to rethink your decision.

Distilled water refers to a type of water produced through the process of distillation.

Basically, this involves heating water, letting it boil and turn into steam, and then cooling it down and condensing it back to liquid.

Distilling water results in clean, purified water free from minerals and other impurities.

The problem is, precisely because of the process it undergoes, distilled water has the lowest total dissolved solids (TDS) among all forms of water.

This means that distilled water is low on dissolved ions, metals, minerals, and salts, which are all important in maintaining aquatic life.

For this reason, you should not use distilled water when changing the water in your fish tank.

Why You Shouldn’t Use Distilled Water for Your Fish

Living in an environment devoid of minerals is extremely harmful to fish for a variety of reasons.

First, it may end up sucking out the minerals out of the fish’s body because of osmosis.

Osmosis is the movement of molecules from a region of high concentration (fish’s body) to low concentration (water without minerals).

This can be dangerous for your fish’s health since they’ll end up lacking the nutrients they need in their body to survive.

Second, distilled water has a pH level that may be detrimental to fish.

Minerals such as magnesium, calcium, and iron help stabilize water’s pH levels.

Distilled water lacks these minerals, making it an unsuitable choice in changing the water in your fish tank.

Suddenly shifting to distilled water can drastically upset the tank’s pH level, which can be fatal to fish.

Lastly, living in distilled water can be biologically destructive to fish.

Distilled water lacks ions (charged particles) from salt, which animals, including fish, use to transmit signals through their nervous system.

Letting fish live in such an environment can severely damage their nervous system, as the salts in their bloodstream can end up dissolving in water via osmosis as well.

can i use distilled water factsin my fish tank

When To Use Distilled Water

Although distilled water makes for a poor living environment for your fish, that doesn’t mean you can’t use them for other purposes.

Here are other ways you can use distilled water:

  • Topping Off Evaporation Losses

Distilled water doesn’t have minerals, making it a good choice for topping off a fish tank.

This way, even if it evaporates, you won’t have to worry about losing essential nutrients in your water tank.

As a result, you also won’t have to concern yourself with breaking the mineral balance in your fish tank.

  • Mixing With Tap Water

If you want to decrease the number of TDS introduced into your tank while keeping a baseline reading, you may choose to mix distilled water with tap or swing water.

Alternatively, you can mix distilled water with tap water to lower the hardness or the concentration of calcium and magnesium ions in your tap water.

  • Replacing Fish Tank Water After Remineralization

Remineralizing distilled water can make it a viable option for your fish tank.

Remineralization requires introducing minerals and other dissolved solids into distilled water to make it suitable for aquatic life.

Having these minerals will counter the disadvantages that typically come with using distilled water in your fish tank.

Distilled Water Alternatives

If you’re not keen on remineralizing distilled water for use in your fish tank, you can use other types of water that are more suitable for maintaining aquatic life.

Any of the following options can be a good choice:

Tap Water

Tap water is the easiest, most convenient option for water in your fish tank.

Municipal tap water, in particular, is typically disinfected for home use, making it free of most bacteria.

This makes for an ideal environment to grow your fish in.

However, it’s still best to check if your tap water is safe before making it your fish’s next home.

Some tap water may have chlorine or trace amounts of ammonia, which can both be detrimental to fish.

Reverse Osmosis Water

Treating water via reverse osmosis means using a filter that traps big particles on one side and allowing water to flow onto the other.

This eliminates potential contaminants, such as larger bacteria, chlorine, and other minerals that may not be good for your fish.

Deionized Water

Deionization uses resins to trap electrically charged contaminants and then exchanges these with harmless ions, like hydrogen.

The resulting deionized water is free from mineral and chemical contaminants, making it an excellent choice for growing your fish in.


Can I use distilled water in my fish tank? As you can see, the answer is more nuanced than you think.

Distilled water isn’t entirely bad, but remember to take sufficient precautions to ensure you’re using it the right way to care for your fish.

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