Thats part of the hobby man, hate to say it but it happens. I just lost one of my goldfish. I change their water often, give them a nice diet, they have enough room but they still got a disease...then another two diseases on top of that. Some people can keep one in a bowl for 5 years....I do it right and loose one. I also lost my breeding pair of fairy cichlids....heater broke and got to hot in the tank. Then I also loose a lot of new fish (bulldog pleco and emerald brochis)...I blame the LFS for that, they don't know how to feed plecos and take bad care of their fish. It sucks but sadly, it happens. There are enough good times to balance out the bad.