If you look at the ingredients of Purple Up,you will notice that all it is aragonite that has been pulvarize.The same goes for Aragamilk which is basically the same thing.
IMO,keeping calcium,akalinity,strontium,iodine at the proper levels as well as moderate lighting and it will come back.Okay,so I really got that from another site.I heard phosphate and nuisance algae inhabit coralline algae growth too..Its normal for bleaching and die-off on new systems but Hawk,I dunno how long yours has been up.