I've noticed recently that my red leg hermits have been dying off in my 10 gallon tank (10 months old). I bought a batch of 10 hermit crabs when I started the aquarium and they lived for about 7 months. After they all died off I bought another batch of 10 and they almost all have died in a matter of weeks.
I don't know if any of these may have caused their deaths;
bicolor pseudochromis (kept pecking at them, die off seemed to coincide with the pseudo being in the tank) (pseudo is now removed)
Short lifespan of small hermit crabs?
carnivorous lettered olive snail (don't think so , but maybe possible?)
Today I noticed a hermit crab which I thought was dead (hanging out of shell, tail visible) but when I went to take it out it jolted back into it's shell. This made me think that the dead hermit crabs may have had an issue molting.
I add trace elements, iodide, and calcium to the tank.
15 lbs live rock
10 red leg hermit crabs (less now)
1 Lettered olive snail
7 Fighting conch