Okay. It sounds like you need to make some changes.
You need more than three inches of substrate- at LEAST over 6. Also, it needs to be moist- in the picture, it looks quite dry. Not dripping wet, but moist enough to hold shape.
You need a heat mat- I'd recommend an ultratherm. Should go on the back wall of your tank. Heat should be 75- 85 degrees F. Humidity is a MUST - you need a way to find out your heat and humidity levels. I'd recommend an Acurite temperature and humidity gauge. I got mine off of Amazon.
Turtle food should not be fed to crabs. A crab's diet needs to include protein, fruits, veggies, calcium, foraging, plant/leaf litter, and more- but that's the "basics". Check these links out:
https://www.hermitcrabassociation.com/p ... 25&t=92554 https://www.hermitcrabassociation.com/p ... 25&t=92557
Crabs also need salt water, as they carry both dechlorinated fresh and salt in their shells. I'd recommend using Instant Ocean, but there are a couple brands out there that suffice. Pools should be deep enough for crabs to submerge in (even though purple pinchers tend to be toe-dippers).
Please also check out this basic care guide:
https://www.hermitcrabassociation.com/p ... 0&t=119273
/hj