How often do fish just up and die?
I prided myself from Fall 2010 until Fall 2012 with ZERO fish deaths of 11 cardinal tetras and 7 corydoras that I had for the year, along with 12 months worth of 4 otocinclus and another school of 8 silvertip tetras (various tanks) . After Hurricane Sandy I had massive casualties as was to be expected with a 40 degree tank temperature and no filtration for 10 days.
Today I discovered a dead silvertip tetra, and I realized it was my first "fish death" that I could not attribute to other causes. I estimate them to be 18 months old plus however long they were in the store (they haven't grown since I acquired them, unlike my cardinal tetras the silvertips seem to be sold as adults or they grow VERY quickly as juveniles).
How often do you find an unexplained fish death and do you worry about it? For the record this is a moderate-heavily planted 40 breeder with 8 silvertip tetras, 2 Eheim canister filters (ie, massively understocked, due to Sandy recovery plan still ongoing).