You need marine salt mix NOT aquarium salt. The kind of salt used for saltwater tanks such as Instant Ocean or the generic variety. You will also need a hydrometer so you can acheive an ideal SG of 1.008. Start with 1 tsp salt per gallon of dechlorinated water and test with hydrometer daily, at the same time every day. Never add salt directly to the tank. When you need to add more salt, remove a bit of the tank water and desolve the salt into the water, then return to the tank. Remember salt does not evaporate so you do not want to add salt when you top off due to evaporation, only when you do your water changes. You CANNOT add any freshwater fish because you are adding ocean salt. You can add fish that acclimate well to brackish such as mollies. Crabs are very sensitive to water quality so you are going to want to cycle the tank completely before adding them. Chances are they cannot make it through a cycle. A sand substrate works best...mine is actually half rocks half sand. Careful with sand..you don't want it too deep or toxic air pockets can form and kill your crabs..make sure when you do your weekly tank upkeep that you stir the sand and you will be fine. They need plenty of land. You can have a sandy beach coming up out of the water, rocks or wood coming out of the water, use a floating island, there are also some really cool underwater islands out there to maximize their dry land space. These crabs need air just as much as they need water so you don't want to underestimate the land space they need. Alot of ppl set up their tanks with only a little water, they don't need much, but I always keep atleast 4 gals in mine. If you can provide a place to hide for moulting both in the water and on land so they can take their pick because they like doing it both ways. A lot of live plants won't thrive with the salt in the water but java fern is always a safe bet.
