We are bound to have a certain amount of mortality in the fish we keep, irrespective of how well we treat them. I wouldn’t be surprised if your fish succumbed to something far more pernicious than ick or fin rot; likely they were just opportunistic infections albeit the most obvious. Heck, sometimes being healthy is the problem. I hear the mortality rate for humans infected with the infamous bird flu is worse for folks in their prime; the immune response is the killer.

Anyway, sorry to hear about your fish. I started keeping plants for the sake of my fish. They are my pets and I wanted them to have an optimal home.