Hey Reebo, sorry to hear about your tank struggles. I agree with the diagnosis of BJD. As an avid euphyllia coral lover, I have seen it strike many tanks before. Did the sick corals seem to strand off into slime strings? If so and it progresses from head to head at random, then my bet would absolutely be BJD. Can be treated with cipro as others have mentioned, chemiclean is also another product I have had success with. You will definitely want to treat. Left unchecked it will be nearly 100% loss of euphyllia and even some other LPS too. But don’t be discouraged it can be beaten to at least save healthy coral!
Below is a pic of one of my 45G frag grow out tanks that was 100% wiped out by BJD, disease started when I recklessly tossed in a colony from a swap because I didn’t have my other QT running. Total progression time was 1 week. Most pieces were already mini colonies rather than frags, but everything infected died, nothing regrew. Thank goodness it wasn’t my display tank.