You don't have one hermit crab that seems to always survive do you? I had a nasty hermit that would kill every other hermit or snail it could get at. I always found my hermits to be almost indestructable and to see your fish and snail doing fine in the pics I would suspect predatation if raising the salinity doesn't do the trick.

Like Mike asked what did you medicate your tank with? Could be the issue.

Also like mentioned your salinity needs to come up, your corals can suffer. I usually tell people to just do top ups with pre-made salt water, brings it up nice and slow :biggrin:

Most people forget that if you're measuring specific gravity you have to account for the temperature of the water too. I find this gets left out very often. I personally prefer the calibrated refractometer method now, I don't think I could go back. With hermit crabs I wouldn't be surprised if they were killing each other as well, they're pretty expendable.

thnks guys for the info and help appreciate it...:biggrin: