With my crabs, I've found the best substrate to be the EcoEarth shredded coconut fiber. Moisten it with a mild salt solution to help prevent molding. This is a great substrate for them to crawl around in, burrow in and it's moist state helps keep the crabitat at a good humidity level. Make sure you are offering them a dish big enough to crawl into and submerse themselves if they want, one of freshwater, one of saltwater. As stated before, lots of various sized shells are essential. They like to climb stuff so try and set up some deco they can climb around on. I feed mine an offering of crushed crab pellets, old fashioned oats (uncooked), veggies, fruits, applesauce is a favorite treat. I use an under tank heater pad that keeps the substrate warm and as it warms the water evaporated and falls back down like drops of occasional rain from the glass top that I keep positioned so it seals all the way around.