How deep is it? And how big is your largest crab? It'd make a very pretty water dish, but the water dishes need to be deep enough for your largest crab to submerge so they can switch out water as needed.
I would say no - the crystals that formed are from water soluble minerals, which means in water they'll start to dissolve again and some of what makes the pretty colors are heavy metals and non-edible elements.
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I used it for a couple days before I read wodes comment, it wouldn't have worked even if I decided to keep it. Those rocks are just like seashells, and once completely saturated water just seeps through it slowly over time. I thought the crabs were crazy thirsty but really it was just the rock leaking the water into the media