Blue2Fyre;4294326; said:Did you clean the filter in tank water?
It is really a good idea to have a test kit on hand for times like these. It's not very expensive and can tell you quickly if there is a water problem or not. Otherwise we are just guessing. Ph isn't very important. The kits you really want are ammonia and nitrite, these are the ones that can kill fish quickly.
It sounds like an ammonia spike but without readings I can't be sure.