since it has oyster shell I would wait until they're at least 18 weeks but if I rinse it out to get rid of the salt would it be ok? Here's the site where I bought it (this was a few yrs ago when we had hermit crabs-boringest pet ever) and it has NEVER been in a tank with a crab (I'll throw the sand from the tank out since a crab or two died in there). There isn't enough to do the whole run but I thought I might put some in the most popular areas. http://www.hermitcrabpatch.com/Hermit-Crab-Crabitat-Substrate-Pre-Mixed-Bag-p/sb030.htm and this is what it says in the description: These 25 lb bags of premixed and moistened substrate mixture are the easiest way to get your tank ready for your crabs. This healthy substrate mixture begins with clean Florida sand. In to that we mix oyster shell and coconut fiber then use Instant Ocean salt water to bring it to the perfect packing consistency.