Pisitils going red can happen for a lot of things. It can happen when pollen, dust, people, etc touch them. Spraying with neem oil likely did it if you sprayed the buds. I thought you were supposed to stop spraying neem once you had buds, but maybe you just have to stop a few weeks before harvest? I would double check. Calmag and bad ph shouldn't have an effect on the pistils i wouldnt think.