i am a tropical fish breeder so i am very familiar with this subject. i have a 4 stage ro/di unit for my fish/plants. this gives me water that has a ph of 6.0 and a tds of 0-2. i will assume that the tds of distilled water hass the same or close tds and i cannot ad any ph down to my 0-2 tds water without dropping the ph so low that it doesn't even register on my chemical ph test kit which has a low range of 4.0.