IMO, no, pH alone would not kill a fish that rapidly.
I think you have several issues going on. To be honest, you have a "shot gun" approach to posting and it is hard to follow what is going on. That is not meant to be harsh, it is true. I really am not trying to be mean.
People try and deal with one "shot" and then there is another thread with different info on the same issue (eg Sly above, who responded in the other thread). He was not being mean, just saying that there is another thread on the same tank/issue - even though the cause was thought to be something else.
Fish are frequently not acclimated and may suddenly experience signficant changes in pH, alk, specific gravity...(eg freshwater dip). Many LFS do not acclimate and I promise you the pH in those bags compared to the new tank is pretty significantly different.
I think you have several issues going on, and the best advice is to SLOW DOWN and post in one thread. IMO, stop looking at new things to buy for now (your title, "I waaaant that" - you may not realize - is not helping you here because it is hitting very close to home and it has personally frustrated me in threads on carpet anemones, sea apples, etc). Otherwise, I am sad (and concerned) to say, future success may be limited.
We are all more than happy to try and help you - both in these issues and in selecting future successful animals to keep. But it is up to you to really appreciate that people ARE trying to help and that you have to facilitate that.