After 10 years with the drop checker, I gave up on it and went the route of a pH probe. It's not that much more expensive at around $40 and you only have to caliberate it once every six months or so.
I went with the Apex ones since I have the controller but something like this is much better and instantanious than the drop checker with it's lag of two hours nad inconsistant and inaccurate readings.
https://www.amazon.com/Temperature-Thermometer-Calibration-Hydroponics-Aquaculture/dp/B08RYJ48X8