What kind of substrate is used in your tank and how deep is it?
Mix of play sand and cocofiber. 6.5" depth in most spots, except where they've been active digging, etc.
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?
Temp/humidity gauges are affixed to a popsickle stick (so that I can move it) at nearly sub-level, and it moves around the tank. Consistently 75% humidity and 85 degrees F in most spots.
3. Is a heat source used in the tank? If so, what?
I have two UTHs attached to the back, with approximately 1.5" of each mat below sub level. I have one small ZooMed, and 1 medium sized.
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 have both salt and fresh water, Salt is mixed with Instant ocean and stored in a gallon jug in a room temp area not exposed to natural light. The fresh is dechlorinated with Prime dechlor and stored the same way. I change their water an average of 2-3x per week.
5. What kinds of food do you feed and how often is it replaced?
Fed on an as needed basis (roughly every other day?), a mix of fresh produce, unseasoned, cooked chicken, and dry krill/shrimp "Turtle treats" from the pet store. I also mix a cuttlebone powder into their dry food.
6. How long have you had the crab and what species is it, if known?
PP, I've had her about 13 months. She has occupied her shell that she came with ever since, despite being offered a variety of size-appropriate shells.
7. Has your crab molted, and how long ago did it happen?
She has molted at least once, but I believe twice. She came up from her most recent molt at the end of June.
8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
they live in a 20 gallon long, with a pet store hinged glass/plexi lid. It is taped in the back (outside) with masking tape to prevent escapes near the air tube.
9. How many crabs are in the tank and about how large are they?
I have 5 in there (now 4 
) Two smalls, two larges, and she was a medium.
10. How many extra shells are usually kept in the tank, if any?
Too many! With the size variety I have in there, I have several of each size shell that are kept in a moss pit. (Not that they stay in there....) Mostly turbo shells.
11. Have there been any fumes or chemicals near the crabitat recently?
Not that I am aware of. I am now worried about the masking tape on the back, although it's been on there for months.
12. How often do you clean the tank and how?
I only really spot clean on an as-needed basis
13. Are sponges used in the water dish? If so, how are they cleaned?
No sponges. I have a large, natural sponge in there that I picked up on a beach in the Bahamas (boiled and dried before I put it in there), but I keep it dry. It does not go in the water dish, it won't even fit. I notice they snack on it sometimes. They also drag it around the tank.
14. Has anything new been added to your crabitat recently?
Nothing new within the past 6 months.
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.)?
I don't bathe them, and I rarely take them out. We watch them a lot thorough the glass, but try to leave them alone as much as possible. We have noticed tiny white mites in that tank within the past month. They do not seem to reside on the actual crab bodies, but I do notice the mites moving on their shells.
16. Please describe the emergency situation in detail.
Unexpected death, preceded by noticeable decrease in activity. All other crabs seem to behaving normally. 
I'm sorry. 
