How to I take care of my fiddler crabs?

fiddler crabs HAVE to have land so just dropping them in there wont work.an undergravel filter cant ave sand so you'd have to remove the sand and put in gravel they have little turtle stands that lead out of the walmart at walmart, petco, and petsmart. if you keep the current filter DO NOT turn on the filter while it is sturred up just wait a couple hours and it should fall to the bottom.