i feel horrible about this but i want an honest opinion. i have lost 3 crabs since this year started.

so i must be doing something seriously wrong. they were in a plastic cage 15"x8"x6" with 1.5" of calci sand. They had a hermie hut that they loved, a large sponge, variations on food, a small tree, and sticks. Their temp was kept at 70, not sure what the humidity was because this was before i got the gauges. Tweek (shy)and Butters (climber) were my first, August 2005. Then I added Token (digger) and Chaos (who was returned for being too aggressive, replaced by Lemi (not afraid of anything). Everyone was fine, then Token stopped digging, got put in ISO and then passed away. About 4 weeks later I lost Butters who stopped moving in general. Recently, about 3 weeks ago, I lost Tweek who crawled out of his shell and passed away. I know that they only come out of their shell to molt or if they're stressed, in which case they die. now i have Lemi, Bebe, and Shelley. Lemi and Shelley are always under the sand despite the temp. Bebe is becoming slower in her movements and doesn't come out to greet you like she used to. i bought a 10 gal glass tank in which they have every shell, the tree, 3 inches of calci sand, 2 hermie huts, 2 sponges, a huge shell of food, lots of sticks that will now be taken out because of mold, and a coconut background that some hermies (not mine now) like to climb and when sprayed helps retain moisture, helping the humidity. what am i doing wrong? why have i lost so many crabs? i feel like i'm a failure at being a crab owner. i just don't understand why they keep dying. i'm scared to get more, because i can't go through another loss. please help me.
