I don't like fish dying off either and it doesn't always happen, the first fish I ever tried was a school of 5 chromis and they all died but two and this was my recent attempt at the school of five and now I have 3. I have only had one other fish die in my DT and it was a blue jaw trigger that jumped out, also had a purple queen anthias die in QT. My tank has been running for a year too and I have some fairly moderate fish to keep I suppose, I have a PBT, green mandarin and a flame angel but there is something about chromis for some reason, everytime I buy an attempt at a school I have 2 die in the first week so just letting you know that it happens although could be the place where I buy the chromis so die that quickly