I did of course reply in your other thread but to answer this q, it's because sperm, both X and Y, are made to thrive in pH in the 7's and anything below pH of 6 kills ALL sperm - both X and Y alike. There is NO evidence whatsoever that X and Y sperm "freeze" in low pH. It's all made up. IF it worked, reproductive endocrinologists would already be using it for a cheaper way to sway gender - they'd just dump some low pH in with the sperm if someone wanted a girl. They don't do it because it doesn't work. :)