Grain Size: The grain size of the sand is an important factor to consider. Hermit crabs need sand that is small enough for them to burrow in, but not so small that it becomes too compacted and impedes their movement. A grain size of 0.5mm-2mm is generally considered ideal for hermit crabs.
Composition: Aquarium sand made of calcium carbonate or aragonite is preferable for hermit crabs because these materials provide a source of calcium, which is essential for the hermit crabs' exoskeletons. Avoid using sand that contains harmful chemicals, such as heavy metals or pesticides.
Depth: Hermit crabs need a deep substrate to be able to burrow and molt. A substrate depth of at least 3-4 inches (8-10cm) is recommended for hermit crabs.
Consider the Type of Hermit Crab: Different species of hermit crabs may have specific preferences when it comes to substrate. For example, some species, like the Strawberry hermit crab (Coenobita clypeatus), prefer a more moist substrate, while others, like the Ecuadorean hermit crab (Coenobita compressus), prefer a drier substrate.
It is always a good idea to do some research on the specific species of hermit crabs you are keeping and their substrate needs before choosing aquarium sand.