I see my post with "
crushed coral" went unnoticed. I would not use sand because it will collapse when the jawfish burrow with it. That is why people who keep jawfish with sand, always have them tunneling under rocks, because they can construct a real burrow. If you have seen them in the wild their burrow will be away from rocks in the sand, but is supported by larger chunks of crushed coral, rocks, shells, etc. They make burrows in the shape of a
volumetric flask, which cannot be support by sand alone.