I bet you are reading your meter wrong. MJ likes acidic soil but usually no lower then 5 so if you are at 4 for wsph and the plants look good you are not reading the right meter or reading the meter wrong is my bet. Lime will stabilize Ph and actually keep it from creeping up. If you want higher Ph ammend with a little baking soda in the water. What kind of guage or meter are you using? And for what application?