The Best Substrate For Goldfish

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Goldfish are one of the most popular fish amongst aquarists. Though they can grow quite large as adults and therefore demand a large tank they can tolerate cold water and do not require a heated aquarium. They are also very commonly found in outdoor, man-made ponds and water gardens.

Choosing the correct substrate for your goldfish is critical because they spend a good portion of their time sifting through it in search of food particles. Goldfish also produce a lot of waste especially as the tank’s temperature increases. For this reason certain substrates are not as suitable for goldfish as for other types of freshwater fish. While having a substrate will improve both the tank’s appearance and your fish’s well-being, using the wrong material can be harmful to your goldfish. In this list we will look at the substrates available to use when keeping goldfish and will point out why some substrates should definitely be avoided.

1. Bare Bottom Tank

Some aquarists choose to go with the bare bottom approach and eliminate all substrate. While this may make it easier to clean your tank, it denies the goldfish the foraging that is a natural behavior of this species. It also leads to a rather drab appearance and will limit your ability to decorate the tank. You will find it difficult to place rocks or other decorations with no substrate to use for stability.

2. Small Gravel

Small, pea-sized gravel is one of the most popularly available substrates in the aquarium world. While it is an excellent choice for some applications, it is not the recommended substrate for goldfish. It may be acceptable to keep smaller goldfish in a tank with small gravel but as they grow the gravel becomes a problem. As the goldfish forage through the gravel, they can be prone to swallowing some particles. This can lead to serious negative health effects such as ruptured digestive tracts. A larger fish is more apt to accidentally swallow some gravel so as your fish grows you will need to replace this type of substrate.

The space between the gravel particles also allows for the copious waste generated by these fish to be trapped. As it decomposes the waste forms toxins at the bottom of the tank. Goldfish spend a lot of time at the tank’s bottom and exposure to these toxins can lead to a degraded immune system and cause your fish to be more susceptible to disease.

3. Large Gravel

Larger sized gravel eliminates the problem of the fish swallowing the individual pieces. Unfortunately this kind of substrate leads to even more and larger spaces between particles where waste can be trapped. This will lead to similar problems with toxins that are harmful to your fish. In general gravel is not a recommended substrate for your goldfish.

4. Soil

Aquarists looking to save money will sometimes attempt to use regular soil as a substrate. While this will not do any harm to your goldfish, their digging and foraging will put this soil into suspension in your tank’s water leading to an unattractive, messy looking tank.

5. Crushed Coral/Shells

Water hardness can be a benefit to the scales and fins of your goldfish. Using crushed coral or shells will help maintain high water hardness levels. These substance should not be placed in the tank as a substrate but instead can used in your filter system to increase water hardness. The crushed coral often features sharp edges that will damage your goldfish as they go about their foraging.

6. Marbles

I have seen marbles used as a substrate in goldfish tanks at pet shops. These environments are not set up for long term habitation. While they are colorful and may give your tank a distinctive look, marbles have all the same detrimental characteristics as large sized gravel. Toxins will be produced and the marbles make it nearly impossible to keep a planted tank. Not recommended as a substrate for a goldfish aquarium.

7. Sand

Sand is by far your best choice of substrate for a goldfish aquarium. Sand does not allow the waste to get trapped below as the waste remains on the sand’s surface. This eliminates the problem of toxins associated with using a gravel substrate. Some gas buildup is possible with a sand substrate, but purchasing a sand designed for aquarium use rather than play sand will reduce these issues. Aquarium sand can be found in different colors though white is recommended as waste products are more apparent against a darker background.

The sand forms a perfect bed for your foraging goldfish. They will dig happily throughout the day as they search for food. The fish may ingest some sand particles but this will not prove harmful. It may even be beneficial to the fish in helping to clear out its digestive system. It has been suggested that the sand can irritate the goldfish’s gills but this idea has been disproved. Sand is also an excellent choice to use when considering a planted goldfish aquarium. Your goldfish will enjoy the addition of live plants and using sand allows for their proper care and placement.

The Best Substrate For Goldfish

Keeping your goldfish happy and healthy should be your goal as an aquarist and finding the right substrate will go a long way in achieving your desired results. Sand is the best choice of substrate when keeping goldfish as it provides the fish with the same ability to forage they would find in their natural environments. It is the best choice when combining live plants with goldfish and will allow all tank inhabitants to flourish.

1 thought on “The Best Substrate For Goldfish

  1. Hi Toby,

    I have had a 33-1/2 gallon long tank with a small gravel substrate, which I now know isn’t good for the fish. I’ve always kept goldfish in the tank, which has been going 25+ years. I’ve always done 50% water changes every other week, vacuuming the under gravel filter each time.

    My last goldfish, who was 14-1/2 years old died very suddenly in February.

    We’re remodeling our home, and had to siphon off most of the water, but not vacuuming, then move the tank to another room. I don’t want to lose such an old biological filter, so have kept the tank cycling ever since we moved it in June.

    I’m now thinking of replacing the gravel with sand, but I’m not sure whether my PowerHead is suitable in this substrate. Also, replacing the gravel with sand will be a huge undertaking.

    What do you recommend I should do?

    Thanks in advance for your help.

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