How to Clean Fish Tank Glass Stains

Keeping a fish tank is a beloved hobby for some people. Maintaining it requires great care and attention. One of the biggest problems every fish tank owner faces is tank glass stains. These stains tend to build-up over time and obscure the fishes from view.

There are two common types of stains, hard water and algae. As any aquarium owner will tell you, water stains and algae build-up are unavoidable. Fortunately, both are quite easy to remove. Most of these methods require everyday household items. We have compiled the best ways on how to clean fish tank glass stains for you.

Cleaning Fish Tank Glass Stains

While hard water stains and algae stains usually have different removable techniques, they share some similarities. It is essential to take precautions while cleaning because you don’t want to harm your fishes or yourself in the process. Read the below steps to find out.

Hard Water Stains

If your fish tank has water with high mineral content, hard water stains can grow in the glass. They are also known as lime deposits and salt creeps. These stains are made up of calcium, sodium salt, and different types of bicarbonate.

When tank water evaporates, it leaves behind white minerals. These stains not only make the tank look dirty and discolored, but you can’t also see your fishes correctly. While cleaning them might seem complicated, it is pretty straightforward. Follow the different techniques given below.

1. Over the Waterline

  1. Take a washcloth or rag and apply vinegar to it. Never apply vinegar directly on the stains because it can trickle down and mix with the tank water.
  2. Use the vinegar-soaked cloth to wipe the stains above the water level. You can get rid of most water stains this way.
  3. Use a dry rag to wipe off the remaining vinegar so that it can’t drip down into the tank water.
  4. While cleaning a lid or other removable piece, rinse it with water to make sure vinegar can’t fall to the aquarium.
  5. If you have stubborn stains, use an algae scraper to wipe them. You can also use the scrapper under the waterline as long as you’ve rinsed the device free of vinegar.

2. Under the Waterline

You can use this method without removing fishes. For lime stains under the water level, use an algae scraper. The majority of the water stains tend to be on top of the water level. However, some can still gather under the degree because of evaporation.

  1. Use the scraper on the inside of the glass to wipe off these stains.
  2. The wiped-off minerals don’t need to be picked up or discarded because they won’t harm most fishes.

3. Removing the Water

For thorough cleaning, you can remove the water and scrape the stains. However, this step should only be followed during extreme cleaning, as changing the water will result in bacterial colonies being discarded, which isn’t ideal.

  1. Remove all the fishes with a net and put them in a backup water tank. Empty the tank water and all the decorative objects.
  2. Use an algae scraper to wipe off the initial hard water stains. Scrub thoroughly.
  3. Make a vinegar mixture of half cup vinegar and a gallon of water. Use a spray bottle to spray the mixture on the lime stains and wipe them off with a rag.
  4. Rinse the tank properly with clean water. Remember to remove all vinegar residues from your fish tank.
  5. Refill your aquarium with fresh water and put your fishes back.


When to Clean: Scrub your fish tank routinely as stains will keep piling up, and it becomes harder to clean the old ones. Try to wipe the glass daily.

Cleaning Products: If you don’t have vinegar, you can use fish tank cleaning products instead. They can be found in pet stores.


Washcloth: Use a fresh rag for cleaning especially one that has never been used with chemicals.

Cleaning Products: Remember never to use cleaning chemicals like window cleaners or other chemicals to remove the stains. Even a drop in those substances can make your fishes sick or kill them. Most cleaning chemicals have chlorine or other elements that are toxic to fishes.

Algae Stains

Algae build-ups are inevitable in freshwater aquariums. Light, nutrition, and carbon dioxide are enough for algae to grow and survive. All these components are found in freshwater tanks. Excessive algae create stubborn glass stains.

You can clean it manually or use an automatic scraper. If you don’t want to clean it frequently, you can also introduce algae-consuming fishes and snails to your fish tank. Follow the below methods and tips for safe cleaning.

1. Sponge

This is an easy wipe-off technique which is also time-efficient. You don’t have to take out your fishes for this.

  1. For slight algae build up on the interior wall of the fish tank, use a sponge to wipe it off.
  2. Remember to use a clean sponge that is free of detergent or any chemical substance because it can mess with the ecological balance.
  3. If you need to scrub extra hard, use a sponge with a coarse side.


2. Algae Scrubber

You can use algae scrubber which is a sponge designed for removing algae stains. Many consider it to be the easiest way to clean tank glass stains because they have a rough side for removing difficult stains.

  1. Scrub from top to bottom
  2. Let the scrubbed algae fall to the bottom of the tank
  3. Instead of picking it up by hand, use your aquarium vacuum to clean it.
  4. You can also use a scrubber with a long handle if you don’t want to put your hand inside the fish tank.


3. Algae Scraper

If you have stubborn interior stains in your fish tank, use a scraper. There is a cleaning device with a scraper and a brush on opposite ends. It’s another product that was made to clean aquariums. You can find one from a pet store or aquarium shop.

  1. Let the scrubbed algae descend to the tank bottom
  2. Use your aquarium vacuum to pick up the discarded algae
  3. Remember not to remove tank water while applying this method. You can withdraw less than one-fourth of the water, but any more than that can ruin the bacterial colonies that have built up over time and your fishes can die.

4. Razor Blade

This step is quite tricky. If sponge or scraper was ineffective in cleaning all the stains, you can try using a razor blade.

  • Hold the blade at 45-degree angle to gently scrape off the remaining algae. If you’re not careful while using it, you will end up cutting yourself.

5. Aquarium Magnet

Some people prefer not sticking their hands inside the fish tanks to clean them. In that case, you can use an aquarium magnet. You can find them at pet shops or aquarium stores.

The magnet has two sides. One side is a scrubbing pad, and the other is the handle to hold on to while scrubbing. Put the scrubber side inside of the tank and move the stem from the outside.

  1. Make sure that your magnet doesn’t go near the sand or gravel at the bottom of tank. If any coarse material gets under the scrubbing pad, it can scratch your glass.
  2. Rinse and clean the scrubber after using it every time.
  • Don’t leave the magnet inside the tank when it is not being used. Otherwise, sand might get stuck under the pad.
  1. If you want, you can attach a piece of felt under the outer part of the magnet. The felt will help to protect the glass from scratches.
  2. Aquarium magnets come in many different sizes. Any size will do for cleaning the tank. But it is better to buy the size that matches your tank because cleaning a massive tank with a small magnet can be difficult.

They also come in different strength modes. They work differently on different types of aquariums. Such as a stronger magnet for glass tanks, a standard magnet for acrylic tanks, etc.

Some aquarium magnets can float. They will float on top even if you drop them. But remove them from the aquarium while not cleaning.

Some magnets have razor blade add-ons to clean severe algae.


Don’t Empty Your Tank: You may think that, for cleaning all the algae properly, it is better to remove the tank water and scrub it all down. If you do so, all the living bacteria that have created colonies in your tank will be eradicated.

After refilling water, it will take some time before these useful colonies re-establish themselves. Putting your fishes back into a cleaned tank with no beneficial bacteria will lead to them dying from ammonia poisoning. Don’t remove more than one-fourth of the tank water if necessary.

Outside Stains

Cleaning the outside of your tank is just as necessary as the inside, but it is more straightforward.

  • You can use a washcloth or soft paper soaked in warm water and gently wipe the outside stains.
  • It is not suggested to use cleaning chemicals to clean the outer walls as there’s always a chance of contamination through the air. But, if you want to, then apply it to the cloth rather than direct spraying into the glass.

Frequently Asked Questions (FAQ)

1. Can I use household cleaning products to remove fish tank stains?

If you don’t have vinegar or can’t find aquarium cleaning products, don’t use household cleaning substances. Use fresh, clean water, washcloth, or scraper only in that case.

2. What is an algae scraper?

It is an aquarium cleaning device that can be used to remove both hard water stains and algae. It is suitable for wiping off stubborn stains.

3. Should I remove my fishes before removing stains?

Most cleaning methods don’t require you to. If you prefer, you can remove the fishes for safe movement while cleaning.

4. Should I empty my tank before cleaning?

It is not suggested to remove your water entirely as it can destroy the bacterial colony. Don’t remove more than 25% water if you can help it.

However, if you want to give your tank glasses a thorough cleaning, take safety precautions and measures to grow back beneficial bacteria.


Whether you have lime stains or algae build-up, the safety of fishes is the top priority. So, remember to take caution while cleaning. Some products, such as the sponge and scraper, can be used to get rid of both stains. Still, aquarium magnets work well for algae ones while vinegar solution removes white stains easily.

No matter which method you use, be very careful not to break the glass and contaminate the water while cleaning. You can remove the fishes before you clean but try not to empty the aquarium if you can help it. Keeping a safe and clean environment for your fishes comes above all.

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