For my crabs (two red claws) I bought a small glass fish bowl and tipped it over inside the tank. It is on its short side and filled with rocks and decorations. I also put an airline inside the bowl. That way there is an air bubble in the bowl with a dry spot on the decorations.

Before when I've had crabs in the tank they always escaped. But since I added the underwater air dome I haven't had any run aways. These guys have been in the tank for 4-5 months now! Before they were in only a short time before escaping

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