I take a much easier route and have had great success. I have been using hydroponics indoors for lettuce, tomatoes, peppers, and herbs for a couple of years. I use one
ebb and flow for the growing stage using the instructions on the GH 3 part for growing, and another ebb and flow for blooming the tomatoes and peppers with the GH blooming ratios.
I usually add a gallon of water with bloom nute ratios every 2 days to the 5 gallon bloom reservoir and a gallon of the grow ratios every 5 days to the 5 gallon grow reservoir. I completely change the solutions every 3-4 weeks.
No meters, no testing and everything grows really well.