Dead molters

[fishbone]

I've lost some crabs during molting and I'm not sure if it's because of something I'm doing. Quick stats on the tank
75 gallon with 6 crabs left
Temp between 72-82 / humidity 75-80%
About 5-6 inches of pool filter sand
Coldest spot bottom of the tank is 70 degrees
I've never smelled dead molters, most recently I've uncovered two empty shells with nothing but exoskeleton left. No stink at all. Based on position of shells (mouth down, leftovers inside) doesn't look like they got stuck under, appears they just died without even trying to make it tops. The crabs were on the small side, she'll opening about half inch.
Does anything in my description jump at you or is this the sort of thing that just happens? So far I've lost 5 crabs this way.

[wodesorel]

so sorry about the deaths. How long had you had the crabs that passed? What species do/did you have?

[fishbone]

They're all PPs. 7 were purchased and 5 adopted. To be honest I'm so hands-off in their caring meaning I don't handle them, I just observe, that I couldn't tell you which are which. Put it this way. I purchased my first 4 on Dec 2008, then 3 in Feb 09 and adopted 5 in Jan 2011. That's a total of 12 and I am left with 6. One was a surface death (dropped his shell and despite my efforts wouldn't climb in one) and the rest perished burried best I can tell. I've had plenty successful molts tho and I can tell at least 2 of the 6 are my originals.

[Rocky]

Lot's of things can go wrong with molting, if they're larger crabs, they need deeper sand so they don't accidentally stumble across a molter while digging around. Also, crabs need lots of calcium and protien, what kind of diet do you feed them? And is your sand at sandcastle consistency? Their tunnels could be collapsing as well.
I'm so sorry about your crabbies We'll figure this out!

[fishbone]

I can tell you with certainty their tunnels collapse. The sand is sandcastle consistency however I think pool filter sand may be a bit heavier than regular sand, I'm not sure. I've never seen their tunnels hold primarily because of the movement of the other crabs. The couple times I HAD to check on molters, what they do is basically they build an empty cocoon around themselves. I can tell you though pool filter sand grain is larger, smoother and does not compact and is virtually dust-free and pure. Afaik it's superior to play sand in every way, but spendy at $15 per 25lb.
Diet-wise I feed them a variety of fruits, veggies and protein. Recently I've started offering them the calcium stuff off The Crab Patch; crushed oysters etc.
Protein wise I feed them almost exclusively commercial foods since I'm not a big fan of stinking up that tank with raw meats. I feed the protein mix the above mentioned site sells and the name of which I forget, dried krill and sporadically Hikari Crab Cuisine. I've also been offering worm casings which they love.
They also have one of those bath corner holders full of coco fiber. They have a couple fresh water dishes and a 3 gallon tub of brackish water in which I see them hang out and bathe occasionally. They seem to love to walk around in it, I see their trails on the bottom sand all the time The tub has a filter and heater in it and there is a cycle maintained. Basically it could house fish/critters at any time.
For lighting I use a Flora Sun 10 (iirc) which btw is probably depleted and needs to be changed.

[fishbone]

Btw I appreciate the help and critical thinking