You can try the following steps to see if they help, It seems streaking is caused by dehydration, a salt imbalance, and/or sickness.

Hermit crabs will naturally hang out of their shell to dry off some of their shell water to make it more concentrated (saltier). Maybe streaking is an extreme form of this behavior that happens when the hermit crab has lost too much body salt and is unable to keep its shell water salty. (This could be caused by too many fresh water baths, or not enough access to a salt source.) Hermit crabs are not that well adapted for life on land so use their shell water to help regulate their bodies chemistry.
The idea of this treatment is to recreate the shell water and re-hydrate the crab at the same time, hopefully allowing the crab to bring it’s chemistry back to normal levels.

Initially, water gain is the priority. A crab without a shell will dry out very quickly, and has probably lost a lot of water already before you discovered it.

Step 1

Rinse a cup several times to get off any residual dish washing detergent. Place the naked crab in the cup with a little fresh water treated with dechlorinator at 75-80 degrees. Not enough water to cover the crab, but enough that it submerges most of the length of its legs, but not the thorax. Offer a shell that is the right size to slightly smaller than usual. Cover the cup with plastic wrap and poke only a few holes for air flow. This will increase the humidity and make it easier for the crab to breath and become re-hydrated. Then place a hand towel over the cup to create a dark environment that will decrease the stress on the crab. Allow the crab to find the shell, or place the crab’s tail in the shell to encourage its reentry (if the crab does not do it on its own). The crab may take from 30 minutes to an hour to get back in a shell. Let the crab rest in the shell for 30 minutes to an hour before filling the shell with sea salt water. If the crab has still resisted the shell after 2 hours, then replace the fresh water with sea salt water in the cup.

Step 2

Sea salt water can be made from 1tsp-1/2 tbs sea salt per cup water. Mix it well and make sure it is about the same temperature as the crab (75-80). Either dunk the crab w/shell into the sea salt water or pour the water into the shell. Do not let this step last too long as it is important to limit handling, which stresses the crab.However, if the crab is not yet in a shell, please replace the fresh water in the cup with sea salt water. Cover the cup with the plastic wrap and towel. Check it periodically to see if the crab has entered a shell, or if it will go in one with your help. Once it’s in a shell, start at the top of step 2. If the crab has not moved into a shell, it is up to you if you would like to do. You can modify step 3 if you like, or try something different.

Step 3

Empty out the cup but for the smallest amount of fresh water it takes to cover the bottom. Replace the salted crab into the cup without spilling too much shell water. Replace plastic wrap and hand towel. Leave the crab undisturbed for 12 hrs (or overnight). If the crab is active (or at least responsive to movements), its chances of survival are good. If it is hardly moving at all, you can continue to let it sit in the cup or try something else you can think of. Either way, it is good to keep the crab in the cup for another half day to let it rest. It has been shown that crabs take longer than 24 hours to fully recover from dehydration. (Don’t worry about feeding the crab)

Step 4

Depending on which environment is better, place the crab back in the main tank or in an isolation tank. Continue to monitor the crabs progress and be sure to put the crab in the fresh water and salt water dishes daily. After about 1 week, or after the crab has regained its full activity level, you may return to your normal general care routine.

Carl

Don’t worry about the sand, the crabs will find the food. Remember, they are natural scavengers so are accustomed to finding scraps of food in all sorts of messy spots.
Of course I’m assuming that the food is not completely buried under the sand!
Enjoy watching your crabs!

Carl

It sounds like you did all the right things. Keep in mind that all you did can also be pretty traumatic to the the crab as well. I would suggest you add several shells to the cage and cover the cage to provide a quiet and dark environment for your crab. Also make sure your crab has a supply of clean water and food.

Best of luck,
Carl