Hermit crab death/molting? issue

[Fighting Conch]

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;
water chemistry
bicolor pseudochromis (kept pecking at them, die off seemed to coincide with the pseudo being in the tank) (pseudo is now removed)
molting issue
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.

Tank:
10 gallon
15 lbs live rock
HOB filter
heater
10 red leg hermit crabs (less now)
1 Lettered olive snail
7 Fighting conch

 

[Smitty]

Are you providing extra larger shells? They don't produce their own and if they don't have larger shells to move into there can be problems (Like outgrowing theirs or having them fight over each others shells).

 

[Fighting Conch]

Yes, there are 10 empty shells from the previous group that died.

 

[Smitty]

Are they larger than the current hermits? Hopefully someone else may chime in here because I really am not sure. I don't know much about the hermits. The other possibility is that they aren't getting enough food. I know they normally scavenge what fish don't get but I didn't see any fish in your list. What are you feeding?

 

[Fighting Conch]

Some shells same size & some larger size, so I don't think it's the shells.
They have been eating raw clam/shrimp meat (uneaten by the lettered olive snail)​

I'll continue to observe one of the molting hermit crabs & see if he molts successfully or dies now that the pseudochromis won't bother/eat him.​

My main concern is that the other inhabitants may start to die if there is a bigger issue that will affect them all.​