"The only reason for using a digital meter is because the tint of the nutrient solution throws off the color test and then your not sure of anything."

Lemon juice, nice and yellow, doesn't interfere with the drops turning the entire solution blood red to show it's highly acidic.

Also, don't use the stupid clear testing tube they give with the drops. Use a white-backed teaspoon.

I'm +/-.2 on my pH with drops versus using a meter. Meters are useless except for PPM, EC, and CO2. Even pH strips work just fine if made in a proper factory.