Why Is My Aquarium Gravel Turning Yellow

Aquarium gravel, also known as the tank substrate, is a material placed on the bottom of the fish tank, where beneficial bacteria reside and break down fish waste, leftover food, and plant debris to keep the water condition healthy.

In this article, we let you have comprehensive knowledge about aquarium gravel and how to fight some problems that arise against the gravel’s well-being.

Why Is My Aquarium Gravel Turning Yellow

You may suddenly notice a yellow tint on your aquarium gravel, making it look less attractive. This may be due to yellow or mustard algae,  which is a form of green algae that has become resistant to chlorine and other sanitizers.

Unlike green algae that float on top of the water, yellow algae bind to some surfaces in the tank, such as the walls or bottom of the fish tank.

Microorganisms such as algae feed on waste products and can taint the water and gravel inside the aquarium. Therefore, the gravel can show a yellowish color. In addition, they can deteriorate the water quality and create an unpleasant odor.

Bacterial bloom can also take place when your fish tank is not clean enough or is exposed to some bacteria that result in the alteration of the quality of the water. The algae and bacteria can negatively affect the aquarium gravel and water, making them look cloudy and yellow.

Another cause of the yellow tint on aquarium gravel is tannin. Tannins are not harmful to aquarium inhabitants as they are natural compounds found in plants. Tannins can be brownish or yellowish. They are also bitter-tasting organic substances found in barks and plant tissues.

However, if tannins leak from the driftwood and plants in the aquarium, they can turn the water and gravel yellow.

Another reason why aquarium gravel turns yellow is decaying plants and organic matter. In a planted aquarium, stray leaves can separate from aquatic plants and float in the tank water.

Without proper nutrition, the aquatic plants will start to wilt. Uncleaned rotting plants and debris look harmless but can build up ammonia and pollute the aquarium water.

How To Remove Yellow Coloration From Aquarium Gravel

To remove the yellow tint from aquarium gravel, it is essential to know the exact cause of the discoloration of water. Therefore, begin with checking the level of nitrites, ammonia, nitrates, and pH of your aquarium water.

At the same time, also look for floating debris, decaying plants, and food waste in your aquarium water. These can be the leading causes of water and gravel discoloration.

In addition, try to look for any decaying fish that is lying or trapped under the decorations or substrate in the fish tank. Rotting fish can also have a negative impact on aquarium gravel.

Another method of removing the yellow tint from the aquarium gravel is cleaning the substrate regularly and frequently. The substrate helps to house the organic waste, food waste, and decaying organic matter. However, this can make the substrate dirty.

So, when you ensure that the substrate is cleaned regularly, it guarantees that the trapped debris does not rot and releases toxins like ammonia and nitrites into the water in the fish tank.

Moreover, regular substrate cleaning can help eliminate pollutants and waste products from the aquarium.

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Best Way To Clean Yellow Gravel

You can follow this guide to clean yellow gravel in your aquarium:

  • Unplug any aquarium electrical equipment and empty the tank.
  • Remove two cupfuls of dirty gravel and set them aside. Because cleaning gravel with chlorinated tap water will kill most of your friendly waste-eating bacteria, it is critical to save some bacterium-containing gravel to re-colonize the tank later.
  • Take the remaining gravel and divide it into two buckets.
  • Fill one bucket halfway with water and turn on the faucet. Stir and rinse the pebbles vigorously until the water in the bucket runs clear.
  • Repeat the same with the second bucket.
  • Warm tap water should be used to clean the tank. Soap should not be used. Clean the filter, thermostat, and tubes as needed. Using a paper towel, clean the inside.
  • Return the now clean gravel into the tank and refill the tank with clean water.

How To Prevent Gravel Turning Yellow

Aquarium gravel can turn yellow due to yellow algae, tannins escaping from driftwood, trash, leftover food, and fish feces.

However, you may take vital steps to prevent and avoid it by changing the water frequently and continually, maintaining the regular and proper water quality, removing floating debris, and adding aquarium filters.

How Often Should You Clean Aquarium Gravel

The frequency or regularity with which you should clean the fish tank gravel is deduced by the pace at which waste is accumulated.

The size of the fish tank, the type of fish, the presence of live plants, the strength of your filter, the number of fish, and all other factors are all variables. When the water chemistry becomes imbalanced, cleaning should be performed on the fish tank gravel.

Will Yellow Gravel Cause Harm To My Fish

Yellow gravel will have no adverse effect on your fish. However, not giving attention to the situation may result in toxicity to the water and cause discomfort to your fish in the aquarium.

If you continue to disregard the problem after several weeks or months, it may result in more critical issues with the fish. The situation becomes more toxic and may lead to fish poisoning and potential death. Taking quick measures is still the best solution to this issue.


You can prevent your aquarium gravel from turning yellow by creating and strictly following maintenance routines. These measures will not only give the fish good health but also prevents discoloration of the water tank, helping to maintain compelling aesthetics.

John Brandon

John has kept fish all his life (since he was about 5). He started with keeping guppies and fell in love with fish keeping almost straight away. That was 40 odd years ago. These days John still keeps fish and currently has two large tanks where he keeps many different types of fish such as Angelfish, Neon Tetras, Goldfish, Guppies and many more.

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