Red clawed Crabs are a brackish crab. To achieve the correct salinity in the water simply add one or two tablespoons of Instant Ocean per gallon of water.
They can tolerate a variety of water conditions and hard water doesn't seem to effect them much. about a 6ph should do for them.
Be sure to keep them in a 70*F to 80*F tank that has 80% humidity, as they require the humidity to breath.
The water should be between 1" and 2" deep. Also provide a shallow dish of fresh water, as they seem to apriciate this once in a while.
The substrate should be either damp sand or peat moss which will support a burrow. The substrate needs to be at least 3" deep to allow them to dig down into it and molt. This is crucial, as they aren't able to molt successfully.
They can be fed shrimp pellets, fish flake food, and fresh fruit. They are not finicky, but variety is best for feeding them.