Help!!

For your PH to have been the cause it would have to be down around 7.6 or 7.4 I forget which level is basically deadly to saltwater fish.
Not to worry you but watch your fish if they had MV in their tanks. It could have spread to the fish you bought because a lot of LFS put a bunch of tank on one sump. Now your tank is at risk of having MV so watch your tank over the next 3 months. I know someone that is dealing with MV as we speak. I can not stress this more we all need to QT fish before you put them into your DT. I know it takes time and the fish don't seem happy in a QT but the other fish in your tank would appreciate it greatly if they did not come down with a sickness. So get a larger tank for your Qt and use the old QT as a hospital tank. I have put fish directly in to my tank in the past (many years ago.)and have lost fish. now I QT every fish that come in my door, I dip all corals.

Bill