Take it from someone that taught a Hort. Sci. class - a pH of 7 for cannabis is not ideal if you use soil. Cannabis, as well as a host of beneficial organisms in the soil, likes slightly acidic soil, no lower than ph 6.2 and generally no higher than 6.8. Anything higher or lower in soil will start to cause nutrient lockout. For hydro, I've had plenty of good results with keeping the pH between 6.0 and 5.5.