Sorry for all your losses. You can use this as a way to learn from your mistakes. Keep doing those scheduled water changes and do them right. Only have as much livestock as your tank and filtration can handle. Soft corals melting away have a link to low alkalinity and imbalanced chemistry. Get a reef test kit and start testing your parameters.
Also, a good heater to use are those titanium ones with the temp probe that is not connected to the actual heater. It gives a more stable temp and well, i have personally never had a titanium heater go "wonky" on me.