The v4 is pretty well a fine powder has higher % Ca, Mg, Fe and some other variation in the micros. Check the MC thread here I put up a pic of the v4 label a few other users put up the v3. I got the part B but haven't used it yet.They also told me that they weren't going to grind up the gypsum balls any more for the one part.
I thought maybe you got an advance relase on v4 and that was related to why you saw improvement at a different pH.