In the three years I've had a SW
tank I've lost three fish:
1 longnose hawkfish - jumped out of tank
1 flame angel - stopped eating
1 royal gramma - old age
I'd say it really has to do with your level of experience with fish and recognizing their behavior and compatability. Fish incompatible with each other will cause stress tank wide and will affect all fish in the tank IMO
. I've had experience working in a hatchery and at Sea World for about 4 years. It also has a lot to do with your setup at the start. If you have the right system from the start, you will have a lot less problems.