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Which Substrates are Safe for Axolotls?

Leucistic axolotl on Exo Terra Riverbed Sand, one of the safest substrates for axolotls, due to its very fine grains. Courtesy of Hikadhei.


We all know that axolotls cannot be kept on gravel or rocks. They feed using suction, and will draw in everything around them, including sand, gravel, and stones that can then get lodged in their stomachs. Sand should be okay though, right? Right! ...Kind of.

Even with sand, there is still a risk of impaction, and that risk increases if you use a sand with a coarse or large grain size. Keep reading to find out which sands are considered safe, and which have a higher risk of harming your axolotl.

In the Wild

In their natural environments of Lakes Xochimilco and Chalco in Mexico, axolotls lived on a substrate of extremely fine-grained silty clay. The image below depicts one of the canals in Xochimilco after a natural event began causing its water to drain in 2017, thus exposing the clay-like substrate beneath the water. The substrate, devoid of small pebbles or rocks, appears to be so fine-grained that it was able to be ingested without causing harm to the digestive system.

Photo credit: Delegación de Xochimilco

Safe Sands

There will always be somewhat of a risk when using loose substrate for axolotls, even if it is the most fine-grained sand on the market. A very soft, fine sand with less than 1 mm grain size poses the least risk, for axolotls over 15 cm (6 inches) long. However, we have even seen axolotls become impacted on CaribSea Super Naturals, one of the safest possible sands out there.

A sand is safest when the grain size is too small to see the individual particles. On the other hand, any substrate with particles that have a diameter over 2 mm is by definition gravel.

Axolotls will always ingest their substrate, whether we witness them doing it or not. When a larger axolotl accidentally ingests fine sand, the grains of sand will usually pass through them without issue.

At this time, we know of a few different types that are very fine-grained:

  • CaribSea Super Naturals Moonlight Sand is considered to be one of the finest, smoothest sands on the market today. It is also available in Sunset Gold color.

  • Exo Terra Riverbed Sand is also very fine, and even advertised as being smooth and small enough to pass through your animals' systems safely.

  • Many pool filter sands also have a grain size of less than 1 mm, and are therefore considered safe. However, be sure to do your research and check the grain size beforehand, just in case! A lot of pool filter sands still have too large of a grain size.

Leucistic axolotl on CaribSea Super Naturals Moonlight sand, one of the safest substrates for an axolotl. Courtesy of Hikadhei.

Unsafe sands

Black Sand

Unfortunately, there are no known black sands that are entirely safe for axolotls. While many people do have enough luck with some black sands, such as Imagitarium, others have found that their axolotls become impacted on it.

Some black sands, such as blasting sand, have even been found to have sharp bits of metal that can leach harmful substances into the water... and some have even been known to rust when placed in water!

Many people have also found that if they wave a magnet over the sand, metal pieces are picked up. Sometimes quite a bit of metal is found! Others have nearly lost their axolotls to severe impaction due to swallowing black sand. Unfortunately, there are no known blasting sands that are a safe size for axolotls, as all exceed 1 mm in diameter.

Play Sand

Play sands are generally considered unsafe because of their unknown origins. Many have been known to drastically affect the pH balance of the water and contain calcium carbonate.

At this time, there is no known play sand, including Crayola play sand, that is aquarium or animal tested. There is a risk of untested sands leaching chemicals into the water.

Play sand is much more coarse than filter sand, since the grains have not been sifted. There have been reports of some types of sand scraping axolotls' sensitive skin and causing injury. This axolotl wasn't able to regenerate properly after being scraped, and finger-like growths began to appear around her stomach injury.

Play sands are typically 2 mm in grain size, which is an unsafe size for an axolotl to swallow.

Axolotl on Axogravel, an unsafe substrate for axolotls. Photo credit: Der Fantastische Bud


Axogravel is another unsafe substrate for your axolotl, due to its size and coarseness. There are several documented cases of impaction and death occurring upon ingestion, and it cannot be detected without a post-mortem necropsy. Axogravel is said to dissolve over time, however it does not dissolve fast enough to avoid getting stuck and impacting the intestines. In addition, it dissolving will also raise the pH level in your aquarium, due to the fact that it is made of crushed seashells.

Safe Alternatives

Image of bare bottom axolotl tank. Photo credit: illiam.

Bare bottom

The safest way to avoid impaction is to remove sand altogether. There is no significant proof that tanks without substrate cause stress to your axolotl.

An axolotl on slate rocks as a subsrate. Photo credit: morecambejim.

Tile or Slate

If you don't fancy the look of a glass bottom tank, then slate or tile, cut to fit your tank and glued down with silicone, are both great alternatives. Just be sure to seal them entirely so that food and debris do not get caught underneath!

An axolotl tank featuring colorful tiles as an option for safe substrate. Photo credit: qwandra


We understand that the topic of using sand, especially black sand, is a touchy matter. We also understand that impaction is not a problem that everyone has been aware of or experienced. However, we feel it necessary to give warning of the risks involved with using these substrates.

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