New hermit owner, worried!

[kpape1993]

Hi. I have just recently bought two hermit crabs August 11th and brought them home. At first they were both VERY active. But one passed away last night. I'm unclear why, it happened so fast. It was moving around ate and drank and then about 6 hours later he stopped moving around. I noticed it actually lost three legs while laying there so I put it in my iso tank. The next morning he had passed. I am very worried that my other one may do the same. And right now my other one is under the sand.

What is the volume of your main tank?
5 gal

How many hermit crabs do you currently have? How big are they?
Now 1 about 1" or a little bigger

How long have you had the hermit crab(s) that you are concerned about?
3 days

What substrate or combination of substrates are you using? How deep is it?
cal sand and jungle bedding by All Living Things. deep enough for them to submerge if wanted.

What do you feed your hermit crabs?
fresh fruit and

Do you use distilled, bottled, tap or other types of water?
bottled spring water and bottled salt water

If you are using a dechlorinator, what brand is it? Does it state to remove all heavy metals, chlorine and chloramines?
none

What brand of sea salt are you using to supply your hermit crabs with salt water?
the bottled salt water

What heat source are you using and where is it positioned?
found a day light heating bulb, have it in on one corner/half of tank

Have you calibrated your thermometer(s) and hygrometer so that you can interpret accurate readings?
yes

What is the air temperature range and humidity inside the tank?
stays between 73-76 degrees.

What is the highest temperature that the substrate near the heat source reaches?
76

Do you have any photos of your tank or hermit crab(s) of concern? If yes, please attach them to your post.
no

[Wai]

The victim may have been subject to a shell fight. Otherwise, it could also be that the hermit crab could not recover from the stress endured in its journey to and in the pet store. Was the salt water pre-mixed by the pet store, or did you mix it yourself? Does it have a brand? Your tank is on the lower end of the ideal temperature range and the bulb might not be enough to heat up the tank for winter in your area. Is it on constantly, even at night, meaning the crabs don't get some darkness? What is the humidity range?

[kpape1993]

The salt water is a premix by all living things. My boyfriend and I were thinking it may be just that, they weren't in a very nice looking enclosure. Right now I am still waiting for the humidity gauge to come in and he has a device coming in to better regulate the temperature. And no I do not keep it on for maybe about 7-8 hours at night so they have their night time. However, we bought a new hermit today because I couldn't have my crab suffer loneliness. Ever since i brought the new one home they have both been out and seem a lot better. My first one hasn't gone back into hiding=].