there is absolutely no reason why PBT tangs cannot be kept easily without casualty.
number 1 cause of death is ich.
with proper quarantine, ich is a disease you can eliminate completely.
study the life cycle of ich.
it is a parasite that you can eliminate for good and prevent it from coming into your system with stringent quarantine.
most people here practice the dump and hope approach where fish bought from fish stores and placed into the tank immediately and then hope that no disease show up.
unfortunately, disease is prevalent in all fish stores and disagree or not, it's there.
many people have the misunderstanding that ich is not possible to eradicate and is part and parcel of reefing but it is not.
if you want an ich-less tank, just quarantine every fish.
quarantine does not mean putting your fish in a betta box and observing. that is not quarantine. that is just as bad as putting your fish in the tank without any treatment.
quarantine is putting your fish in a separate tank and treating it for disease and only once it is disease free, then you place it in your tank. most people in singapore do not have the space or time for quarantine tanks and that's unfortunate, like me. i don't practice quarantine too.
but if you don't quarantine, then ich will always be a problem. it will always be there. but it is NOT impossible to get rid.
the next best thing will be to obtain healthy fish, stock slowly, under stock and feed your fish well. you will still get some kind of ich outbreak but the severity depends on your discipline and your maintenance.
you will never get rid of ich unless you quarantine all your fish from the start. that means before you put any fish in the tank since day 1.
that doesn't mean that ich is incurable. it is not found everywhere.