Shallow tunnel collapse

[Mellee88]

Hello, new crab owner here. I brought home 4 crabs from the beach in hopes of giving the lil guys a proper habitat. I set up a PPS tank for them in hopes that it would be good for them until I get their larger tank fully set up. It took me about two weeks to set up their new tank. Their pps tank only had two inches of substrate in it to hopefully prevent molting. By the end of the second week the crabs began pushing the substrate around and making little hills to bury themselves in. Two of the crabs changed shells and remained very active, and the other two dug themselves into the mounds. I have a large seashell half buried right between them so they shouldn't come in contact with each other, but I can tell they are shifting around. One of the mounds cracked open, and you can tell the tunnel he made has collapsed around him and I can see the top of his shell from the crack at the top. I have since set up the new tank and transferred over the two crabs who were active, now I am just waiting on these two to resurface. Should I be worried?

[curlysister]

This is the biggest reason I would recommend against a PPS tank - if a crab needs to molt, it can't put it off until we say they should molt. So you end up with crabs surface molting, or close to it.
If the tunnel has collapsed, the crab will suffocate. I would recommend digging him up and isolating him with his exo until he has eaten it and is moving around normally.

[Mellee88]

I dug them up today, I had just started smelling a nasty fish smell coming from the tank so I was expecting to find a dead crab. As soon as I scooped a bit of sand away one of my little guys shot out of the sand and scurried around. My other had finished shedding his exo and had eaten all but the big claw and two legs. I have him isolated with the rest of his exo, some new shells and some food and water. He has walked around in a few circles, ate some of his exo and in now taking a nap. I'm hoping I can move him back into main tank soon.

[curlysister]

Sounds good!

[HermitCrabFreak]

This is the biggest reason I would recommend against a PPS tank - if a crab needs to molt, it can't put it off until we say they should molt. So you end up with crabs surface molting, or close to it.
If the tunnel has collapsed, the crab will suffocate. I would recommend digging him up and isolating him with his exo until he has eaten it and is moving around normally.

How can you tell if a tunnel has collapsed? Just curious if there is a way to know for sure. That is always something I worry about. My sand is the perfect sand-castle consistency, but I still worry.