I think ghost shrimp are much hardier that amano shrimp, at least they are supposed to be. I've heard Amano shrimp are not forgiving for bad water conditions, although there seems to be some debate on their nitrite and nitrate tolerance. My amano shrimp have molted and are still fine.
Are you treating you tank with algae medication? Usually it contains copper and that kills invertabrates... Actually alot of fish medication also kills shrimp.
About what algae amano shrimp eat, I think they primarily eat hair and string algae, not quite sure though.
20G heavily planted tank with Eco Complete
Pressurized CO2, Eheim Ecco 2236, 1 55W and 1 36W bulb