1) How big is your tank?
2) What type of cray is it?
3) What is you SG currently, I'm assuming 1.000 (pure water)
4) Do you own a hydometer? If not, get one. I prefer the floating ones over the swing arms but I use both.
5) What type of salt do you plan to use? It has to be marine salt, not aquarium salt.
Raise your SG by .001 per week and check it with your hydrometer. To figure out how much salt you need to add, I need to know your tank size and what not. I hope this helps, PM me with any questions, or just send me the mono and I will take care of it. It would fit in nicely with my community.
I bought a mono and a scat in July at the same size. The Scat grew twice as fast, and stopped being shy. The mono went from agro to passive and died