How to Remove Hard Water Stains from Aquarium?

An aquarium filled with colorful fishes and unique décor completely transforms a room.

Whether you place it in your living room, in the waiting area of your office, or in a corridor of an entrance hall – an aquarium can instantly perk up any place.

However, this is only true if the cleanliness of the tank is regularly maintained.

Unfortunately, hard water starts accumulating, leaving behind stains that make the glass look dirty and stained. This mostly happens if high-mineral water is being used in the tank.

These stains make the tank seem discolored and dirty even if the water inside is clean.

Removing hard water stains seems like a daunting task but with the right techniques, you can easily clean up the aquarium.

Fortunately, there are various tips that will help in preventing these hard water stains and ensure that your aquarium looks stunning all the time.

Read on to find out everything you need to know about how to remove and prevent hard water stains from your aquarium glass.

What Causes Hard Water Stains in Aquariums?

While hard water is safe for you to drink and is also an ideal habitat for most of the fishes, it is not too good for the aquarium.

Hard water gradually leaves behind a white residue on the surface of the tank.

This occurs when the mineral-rich water starts evaporating. As a result, it leaves behind the minerals that get stuck on the glass.

This buildup is referred to as hard water stains.

These stains don’t hurt or cause any damage to the fishes or the tank, but they look unappealing.

These stains also make it hard to see the beautiful fish and tank décor.

Steps to Remove Hard Water Stains from Aquarium 

Following are some easy steps to follow to properly clean hard water stains, leaving the aquarium sparkly clean:

Step 1: Preparing for the Cleaning 

Start by prepping the aquarium for the cleaning. It is not necessary to remove your fish from the tank, especially if it is large in size.

The fishes will move to another area as you start the cleaning.

Removing the fishes from the tank frequently also stresses them, which is why it is ideal to clean the aquarium without removing them.

However, if the water stains are tough and you are conducting a thorough cleaning of the tank, removing the fishes and placing them in a backup aquarium is better.

Gather up your cleaning materials, including a clean soft cloth, a scrub, and a cleaning solution.

Step 2: Pick the Right Cleaning Solution 

There are several cleaning solutions that you can use to remove the hard water stains. Here are the four most effective ones:

White Vinegar 

Vinegar is one of the most effective cleaning solutions for various objects.

It effectively loosens up the deposits, buildup, and stubborn stains since it is acidic in nature.

The best thing about white vinegar is that it is natural.

Unlike other chemical cleaners, using white vinegar as cleaning won’t harm your lungs or eyes while you clean, nor will it harm the fishes.

Here is how to clean the hard water stains using white vinegar:

  1. Combine vinegar with lemon juice as this will enhance its effectiveness and leave a pleasant scent.
  2. Make this mixture in a spray bottle and warm it up by microwaving it for about 20 seconds. A warm cleaner is more powerful in removing stains as compared to room temperature or cold cleaner.
  3. Spray this mixture on the aquarium glass, directly on the hard water stains. Leave it for about three minutes.
  4. Wipe it off using a clean paper towel or a dry cloth.


Toothpaste is another effective natural cleaner to remove stains from the aquarium.

And I am sure you can find it lying around somewhere in your house.

Here’s how you can use toothpaste to remove hard water stains from your aquarium:

  1. Squeeze out a small amount of toothpaste on a slightly damp paper towel or cloth.
  2. Target the stains one at a time by rubbing the paste on them in circular motions.
  3. Apply more toothpaste as needed.
  4. Leave the paste on for a few minutes.
  5. Make a mixture of vinegar and water to wipe off the paste.
  6. Then use plain water to wipe away any residue.

Acidic Cleaner 

Hard water stains are alkaline, which is why using an acidic cleaner can do wonders.

There are plenty of aquarium cleaners that also target hard water stains.

Be sure to opt for a cleaner that includes withering hydrochloric acid, sulfuric, or phosphoric acid.

These chemicals are most effective in breaking down stains and residue. Apply the cleaner as per the directions on the label.

These cleaners are toxic, which is why you must take the right safety precautions when you use them to clean your aquarium. Wear protective eyeglasses and gloves.

It is ideal to remove the fishes from the tank if you are cleaning it with an acidic cleaning product.

Water and Salt Mixture 

Combining water and salt also helps in loosening up mineral buildup and tough stains.

The salt act as a scrubbing agent, which cuts right through the hard water stains leaving a cleaner surface.

  1. Spray this mixture on the stains.
  2. Use a clean paper towel to wipe the area using circular motions.
  3. Thoroughly rinse the area with clean water.
  4. Wipe with a clean cloth to remove any residue.

Step 3: Scrubbing the Tank 

Using the cleaning products above will most likely clean the hard water stains, and any other buildup from the aquarium.

However, if the stains are stubborn and tough then some scrubbing can help in loosening them up.

Be sure to use soft scrubbing sponges when scrubbing the surface as to not scratch the glass.

Moisten the stains to remove as much buildup as you can carefully, before using any of the afore-mentioned cleaners to clean the stains completely.

  • Baking soda can be utilized as abrasive for the scrubbing. However, be sure to use soft brushes or other tools.
  • For a particularly tough stain, you can use a blade to scrape the buildup. You can use an algae scraper or razor blade to gently remove the stubborn stain. Make sure you are wearing protective gloves when using these tools to prevent any cuts or abrasions. It is best to moisten the area to make it easier to use a scraper.
  • However, if you have an acrylic tank then avoid using any kind of blade as it will easily scratch the surface.
  • After you have scraped the glass or/and scrubbed the surface, make sure you thoroughly rinse the area. You might have to repeat the process a few times to get the stains off. Afterward, use a cleaner to wipe off any residue to complete the cleaning process.

Step 4: Cleansing the Tank 

Once you are finished removing the stains from the aquarium by using a cleaning product and/or scrubbing technique then you need to prepare the tank for the fishes.

Thoroughly clean up the aquarium using only clean water and wipe the sides.

Afterward, remove the dirty water from the tank. Utilize a gravel siphon or switch on the self-cleaning tank option to cleanse the tank and remove any potential residue.

Let the tank dry off properly. Use a clean cloth to clean both the outside and inside of the aquarium for that extra clean shine.

Keep in mind that you have to replace at least 10% of the water weekly to maintain a healthy environment for all the fishes.

In case the fishes don’t look active or you notice the fins tucked in then you must replace around 25% to 50% of the water.

Fishes need clean water to stay active and healthy. Keep monitoring the aquarium regularly.

Step 5: Fill Up with Fresh Water 

While you might be tempted to fill up the aquarium with purified water which is available in grocery stores, there are numerous minerals in tap water that get filtered out during the purification process.

Therefore, it is recommended to use fresh tap water.

Before refilling the aquarium, leave the water quantity you want to refill overnight without covering it.

This will evaporate the chlorine content. Using room temperature water will become too warm from the fish, so it is ideal to store it in a cool place before you refill the tank.

Add some freshwater salt in the water as this helps in preventing diseases and maintaining the health of your fishes.

Another thing to keep in mind is that the water you are about to refill should be the same temperature as the tank.

Use a thermometer to determine if the temperature is right.

To avoid messing up the décor in the aquarium, fill a bucket with water and place it above the tank; then utilize a siphon to carefully fill the tank with freshwater.

These steps will ensure that all the hard water stains and mineral buildup are thoroughly removed from the aquarium.

Tips to Prevent Hard Water Stains from the Aquarium 

Investing long hours and efforts in scrubbing out hard water stains from an aquarium is definitely not a fun task.

The best way of avoiding this is to reduce the chances of hard water buildup.

Follow these simple techniques to prevent hard water stains from aquarium glass.

Targeting the Source 

The most effective way of removing hard water stains from the aquarium is intervening before this problem even occurs.

This can be done by targeting the source. Here is how:

  • Since these stains are caused due to the evaporation process, monitor the water line regularly. Once you notice the water has started to evaporate, refill it with distilled water. While hard water is ideal to fill up the tank, if you replace the evaporated water with more hard water, it can cause a lethal increase of some minerals. Therefore, use distilled water to eliminate the stain problem, without causing another issue.
  • Maintain the right pH balance (and KH Balance) and level of minerals in the water.
  • Eliminate excessive minerals by using a filter.
  • Water softeners are another effective means of counteracting hard water.

Regular Cleaning 

As mentioned before, regular cleaning reduces hard water stains.

Even if the stains do appear, regular cleaning stops them from becoming stubborn.

  • Be sure to clean up the glass surface from either side.
  • Ensure excess hard water is regularly removed from the aquarium.
  • Clean the glass surface weekly and do a thorough cleaning every three to six months.
  • The longer the hard water stain stays, the more effort you will have to put to remove it. Therefore, clean the tank regularly.

Consider Self Cleaning Tanks 

Opting for self-cleaning tanks is an ideal way of maintaining the cleanliness of the aquarium and preventing hard water stains.

The process is fairly simple.

You just need to ensure that the attached pump is working perfectly fine by switching it on and placing a cup underneath to collect the dirty water.

Once the self-cleaning is done, throw away the dirty water, and fill the tank with freshwater.

The pump is gentle and won’t bother the fish, so you won’t have to go through the process of removing all the fish from the aquarium.

Replacing Filters

Replacing the filters or the cartridges in the filters regularly is also required to maintain the cleanliness of the aquarium and reduce the hard water stains.

Be sure to follow the instructions and guidelines of the filter regarding the right time to replace or change them.

Generally, the cartridges must be changed monthly.

While the filters will be cleaned during your weekly or monthly cleaning process, this will not help in extending the life of the filters.

Therefore, replace or change the filters as per the specified guidelines.

A properly cleaned and well-maintained aquarium helps in extending the health and longevity of your fish.

Moreover, the sparkly clean glass of the tank will look stunning in the room as the fishes and the aquarium décor will clearly be visible.

Keep on monitoring the fishes to identify and prevent any potential problems.

It is highly recommended that you follow the prevention tips to avoid going through the long process of removing hard water stains and mineral buildup and to ensure the aquarium stays spotless.

You may also like the following articles about aquariums: