I used citric acid, which you can probably get in an old fashion type drug store--if you can find one--but you have to be very careful using it because it can really alter the formula--I wasted several expensive shampoos trying to lower ph & nothing was satisfactory so I stopped playing chemist. Too much flattens hair, which looked dreadful, & you must wash again to remove. I used strips to ascertain what level I had lowered it to--it's a paper strip like you use to test the ph in a swimming pool.