New hermit crabs from the texas city dike?

I recently brought 10 hermit crabs from the texas city dike home. I put them in a 10 gallon tank with some of the water from where I got them. Their bodies are grey/tanish with black stripes and two equally sized pinchers. I have a lot of questions about them. First off can you take a crab from the beach and treat it like a pet? I don't understand what the difference in a beach hermit crab and a pety shop hermit crab is. second i don't think they are eating. I have tried putting a lot of different things in the tank but they don't eat. I tried rice, potatoes, meat, bread, fruit and all kinds of stuff. Sometimes they make a clicking noise and vibrate the wateer. I don't know if they are filtering the water or what. Idk if they are filter feeders or if they eat other foods. also should I have a lot of water (fresh water or sea water???) or mostly sand(dry sand or wet sand???)