HCA: Hermit Crab Association

I just bought a new crab for my 30 gallon tank, its a small crab, but very active. I know im supposed to isolate it, but how long? Also am i supposed to give it a “bath” before adding it to my new tank? Thanks!

Most of us don't isolate new crabs. Just give them a look over to ensure there aren't any mites attached (which would be extremely rare), and pop them into the tank. We don't generally recommend bathing crabs, but a quick dip in the fresh water for your new crab and the existing crabs will ensure that everyone smells the same and nobody seems like an intruder.

Okay, thank you.
A few more question, sorry… should i put the crabs old shell in the tank(she changed as soon as we got back) its glazed so im assuming not… just checking because im not sure whats best. Also should i put her in the main tank before i go to school or wait until i get home to introduce her/him.

I would probably wait until you can observe them for a bit, so after school would probably be best. Watch them for a bit, then check in on them a few times during the evening. That way, you can separate them if there is any bullying.
Are you sure the old shell is glazed, and not just polished? Polished shells are very smooth and shiny, they look like they have a protective coating on them but they are just natural shells that have been polished up. If it's just polished, I'd probably put it in so he has the option of changing back if he has buyer's remorse about the new shell.