I don't use pH 'drops' but by this time I'd be looking at another way to validate the pH readings. I bought a rapidtest analog pH tester and a rapidtest digital pH tester for my brother. Both were entirely useless. I bought the rapidtest capsule tester and I couldn't get any useful info from that. I borrowed a Milwaukee pH tester and calibration solutions and that worked so I bought a Bluelab pH tester and solutions as it was highly recommended. I would recommend this unit for you. I have been using General Hydroponics pH down to adjust the water/nutrient solutions. It takes a while for the pH to settle out after adding nutrients or pH down so take that into consideration.