HCA: Hermit Crab Association

My crab has buried himself yesterday morning and he didn't came up last night. Now in my tank I have a ocean smell like salty air. Is he de stressing, molting or dead

I know I ask a lot of questions but I reaaaaally don't want them to die

He could be de-stressing, molting, or just digging for fun. Digging is a very, very normal thing for a crabbie to do. Depending on the crab and the reason they've dug down, they can be under days, weeks, or even several months. Try not to worry.