By high pH do you mean very high acid?Simply put-pH is a measure of ions and the lower the pH the more acidic and the higher the pH- less acid. A better measure of its need is the TA of the must. If you don't have a TA above about a 6, it really doesn't accomplish much. There just isn't enough Malic acid in it to convert to Lactic acid to make it worthwhile.Is this must a red or a white- grape or something else. These factors all make a difference. MLF is not a cure-all, but does have it's place if needed. You can get the dry and rehydrate yourself, but small packets are hard to come by. The large packets are expensive and do about 60 gallon batches. The liquid makes the process easy.