Thank you for your reply. However, grapefruit juice (it's what you mean by GFJ, right?) is citrus, so I can't use it. I've tried that before, years ago, and the mixture sat in my stomach all night. I got into terrible pain, vomited with a lot of pain, had some relief until the pain returned and so forth. It was a nightmare. Recently I found out that I have Histamine Intolerance , and upon trial I learned that I react to citrus fruit, so that's why. Hence my question.
If it's only about the acid, vinegar would be fine. If it's about citric acid , I could buy that and use it, as I don't think I react to that.