Question regarding my crab

We purchased our crab,Freddy (my son named him or her) 7 months ago for my son at beach shop in Ocean City,MD. He or she is always hiding and only comes out at night usually past midnight. My question is do you think his set up is ok and his tank too small. I want to buy another one because I feel it maybe lonely. Also I can't tell if he likes this food, I refill it every few days. The pool is salt water and the other one is fresh water. These are pics I managed to get of him last night when he or she was active and today. Any advice is greatly appreciated.