Also don't panic too much. The important thing is finding the root of the problem as there are plenty of us in the club that can help you replace them.
Again the RTN on two corals side by side could b a domino effect, in which case getting the RTNing coral out could help and in a sense solve the problem. If however it is something different, as in something in the water or from the softies, fragging might help in the short term but in the log term they would be gonners unless yu fix the problem.