How to Install an Under-Gravel Cave in an Aquarium or Terrarium

By Nathan Trowbridge · Mossari

An under-gravel cave creates a concealed chamber beneath substrate while keeping entrances accessible. The Mossari Under Gravel Cave has an open bottom and two upper access openings. It can form an underground shelter in a freshwater aquarium or a suitably planned terrestrial enclosure.

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Can I add it to an established aquarium?

Yes. The product’s installation method uses the open bottom to limit excavation to the area inside the cave. Check your chosen spot for animals, plant roots, buried equipment, and supporting structures before disturbing the substrate.

1. Rinse the cave and inspect the openings.
2. Position it against the aquarium’s front glass.
3. Press it carefully into the gravel, sand, or appropriate substrate.
4. Use an aquarium siphon through an upper opening to remove substrate trapped inside the shelter.
5. Leave both upper access openings slightly above the substrate and keep routes clear.

Work at a pace suitable for your aquarium. Do not undermine heavy rocks, uproot an important planting, or force the cave through an animal’s hiding place.

Should I completely bury it?

You can conceal much of the structure, but do not obstruct the upper openings. A cave full of trapped substrate does not provide usable shelter. Check entrances after maintenance and as loose substrate shifts.

What size should I choose?

These overall dimensions are not a guarantee of entrance clearance.

Compare the animal’s adult size with usable openings and interior space. It should enter, turn, and exit comfortably. A juvenile that fits today may outgrow the cave. Do not choose by species name alone.

Is it suitable for Corydoras or shrimp?

The product was originally designed as an under-gravel Corydoras shelter and lists small bottom-dwelling fish among its uses. Suitability still depends on the actual animal and placement. Provide appropriate overall habitat and observe use without forcing an animal inside.

How is terrarium installation different?

Place the cave on the enclosure floor before adding substrate, then arrange the substrate around and over it while preserving entrances. Use substrate, moisture, and temperature conditions appropriate for your species. A hide’s shape does not make it suitable for every tarantula, reptile, or invertebrate.

The listing includes terrestrial applications such as tarantulas and appropriately sized reptiles. Check species-specific husbandry and adult clearance. Keep PETG away from direct contact with high-temperature heating equipment.

How do I clean and inspect the cave?

Mossari specifies rinsing before installation and cleaning with water and a soft brush. Avoid harsh household chemicals and abrasive tools. Keep the chamber accessible for inspection and removal; check for animals before moving it.

Under-gravel cave or Catacomb cave?

The Catacomb Skull Cave adds a visible decorative skull motif with a curved shelter profile. The under-gravel model is intended to create a concealed chamber with upper access openings. Choose by placement, access, and animal fit rather than decoration alone.

See the Under Gravel Cave and plan the entrances and maintenance access before installing it.