It sounds like you found some pieces of exo that were not eaten after a molt. Don't panic. There are some things that can be improved in your tank though.
Great advice by Crabby33, just adding a few things to it as well:
1. What kind of substrate is used in your tank and how deep is it?
I have a 10g tank and use EcoEarth for about 5 inches and calcium sand for 3. In th middle is a small strip of standard wood chip reptile bedding. It has created small pools of water. The substrate is approximately only twice the height of my biggest crab but I was planning on deepening it this weekend.
First of all, Calcium sand is a big no no for hermit crabs. It’s not a safe sand and it’s expensive. Children’s play sand is cheaper and safer when mixed with Eco Earth. You need to remove the calcium sand and get play sand. Home Depot, Lowe’s, Walmart, and Ace Hardware all carry it. It can be bought for $5 for a 50 lb bag.
Curly - Agree that the calcium sand needs to go; it becomes hard like cement when it is wet and can kill crabs. Many of us use a mixture of playsand and EE in a 5 to 1 ratio. It needs to be at least 6 inches, or three times as deep as your largest crab, whichever is deeper. It needs to be mixed with dechlorinated fresh or dechlorinated salt water so that it is 'sand castle' consistency, so it holds it's shape without being so wet that there are pools. I would do away with the wood chips completely
2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?
I use a ZooMed digital hygrometer and thermometer. It usually read 80℅ and it is usually 82°.
3. Is a heat source used in the tank? If so, what?
I used a heat Lamp on the top of my tank.
This forum does not recommend heat lamps. Most peoplep prefer to use UTHs. Placed on the back, not under. I use a heat pad for people, also placed on the back. This helps to heat the air in your tank, which is what you want. Never put it under the tank. Hermit crabs are obligate burrowers when they need to tunnel to make their molt caves.
4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?
I use a ZooMed salt water and drinking water dechlorinator.
The ZooMed salt water and drinking water dechlorinators are not appropriate for hermits. It’s recommended to treat tap water with Prime for your fresh and salt water ponds.
Curly -Unfortunately, lots of products that are labelled for hermit crabs actually aren't safe for them. As stated, most people use Prime to dechlorinate tap water. Marine salt then needs to be mixed in to create salt water, Instant OCean is the brand most of us use. Pools need to be deep enough for crabs to fully submerge, but there also needs to be a way for them to climb out (ie- ladders of plastic mesh or similar).
5. What kinds of food do you feed and how often is it replaced?
I replace the food everyday. I feed them carrots, apples , honey and hardboiled egg.
You need a little bit more variety. My crabs love freeze dried insects like crickets and mealworms. Even canned grasshoppers will work. But also offer fruits, vegetables, seeds, nuts, etc.
Curly - check out the posts that are 'pinned' to the top of the Food & Water section. They discuss a balanced and proper diet. Crabs need protein and a source of calcium every day.
6. How long have you had the crab and what species is it, if known?
I have three crabs, Tito, Frito and Cheeto, they are all PPs. I have had them for about 2 months.
7. Has your crab molted, and how long ago did it happen?
No confirmed molt but I put a post in the Molt section.
8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
They have a 10g glass tank with a netting lid that is covered with saran wrap. There is no hole.
This forum does not recommend a 10 gallon as a starter tank. 20 Gallons or bigger is what we recommend.
Curly - a ten gallon can work, depending on the size of the crabs and how many. Here is the HCA Tank size and Crab Size guide:
http://www.hermitcrabassociation.com/ph ... 26&t=92541
9. How many crabs are in the tank and about how large are they?
3 purple pinches. They are all different sizes. Two are small and one is medium. Except one of the small is snaller than the other.
This forum considers 3 crabs in a 10 Gallon tank overcrowded. I have 2 in a 20 and that is enough space for them to molt and grow.
10. How many extra shells are usually kept in the tank, if any?
I keep about 3-4 shells in there.
You also need more shells. Since you have purple pinchers, turbos are the most recommended shells and you need 3-5 per crab, although there are exceptions. I have a PP crab that prefers D shaped openings and won’t wear turbos.
11. Have there been any fumes or chemicals near the crabitat recently?
12. How often do you clean the tank and how?
I spot clean everyday and deep clean sporadically depending on how dirty it is or other things. I am planning on deep cleaning tomorrow but
Just stick to the spot cleaning. This forum does not recommend deep cleans.
Curly - Only spot cleaning the poop and bits of food that get dragged around the tank is needed with proper substrate. However, it might not be a bad idea for you to remove all the substrate in your tank and replace it with proper sub, given that there is calcium sand in it. Then after that, you won't ever need to remove and replace all of it. I have had my crabs for 8+ years, and have upgraded tanks twice, and have never thrown it all out - I have just added more as needed.
13. Are sponges used in the water dish? If so, how are they cleaned?
Yes. I have one sponge and I boil it in dechlorinated water.
Ditch the sponge. Sponges are an old practice and are no longer recommended.
14. Has anything new been added to your crabitat recently?
15. Is there any other information you would like to share that might be helpful (anything that is regularly part of your crab care, playtime, bathing, etc.)?
16. Please describe the emergency situation in detail.
Last night, I heard some serious clicking and clacking of shells. In the morning I found and empty shell and a crab on my net. I have a saran-covered net top and Cheeto was hanging from it. He has never done this. Later today, I discover my 2nd crab, Frito up there as well. I was expecting a bloodbath, and so I removed the large obstacles from my crabitat. Under a large fake shell, I discovered pieces of a shell. Fearing the worst, I checked all three of my crabs but all 18 front legs and claws were accounted for. I haven't found the entire molt, nor any larger pieces. Tito's old shell is still sitting there and nothing further has happened. There have been no additional fights and they are simply walking around like normal.