Didn't have time to do a full testing of the 120g as promised because I was in hospital for the last week
Chris was looking after the tanks while I was gone and I noticed he hadn't been topping up the tanks very well. At least he was feeding the fish and topping up a bit
Found only one dead snail upon my return today, but that one may have been there for awhile.
Anyway, was making up new water for the water change this weekend and noticed I'd been reading my refractometer incorrectly
Tested the 120g and SG was only 1.020
When I think back to when I got the refractometer, I'd say the snail deaths may have started a month or two after getting it.
Have spent the afternoon removing half buckets of water from the tank, adding salt, stirring thoroughly, then putting that water back into the tank. So far, am up to 1.023.
So, I'm thinking low SG must have been the cause of the snail deaths. The clicking sound is probably a harmless alpheid shrimp or something similar, and cr*p, do
I EVER FEEL STUPID 