HCA: Hermit Crab Association

A newly adopted crab evacuated his shell and began to surface molt a couple days after getting him. I was able to isolate him in a critter keeper that is being kept in my main tank. He is back in a shell and has eaten all of his exo! I have provided him with food and small amounts of both fresh and saltwater.

It has been about 9 days since I first isolated him. I think he's been drinking some of the water and moving around a little bit. But he doesn't seem to be very active yet. I'm wondering, what signs should I look out for to know when it's okay to release him from isolation? I have 2 other crabs in the main tank as well.

It was so scary to deal with, but I'm very happy he survived such a stressful situation!

Yay for him surviving!
I'd recommend things that are considered high in energy, such as honey! It'll help him get more energy to move around! I've also heard of adding the sea salt mix you use for the sea water (instant ocean) to help with minerals. Giving lots of protein and calcium is very important at this stage!
But if he's moving around, and has all of his energy restored, then I'd say let him go back into the main tank!

I'd wait until he is moving around 'normally', so when you think he's as active and strong as he was before all this happened.
Also keep in mind that crabs who surface molt, do not 'scrub' off the molt smell like and underground molting crab does when it digs back up to the surface. You may want to consider dipping everyone in the fresh water quickly, so that they all smell the same.