My experience is similar to yours. I have had two Hanna HI 99104 meters go bad on me. I used them to measure the pH of my color chemistry and they went bad after maybe a couple dozen uses or so, measuring mainly developers. They just wouldn't calibrate anymore. The instructions said to rinse with water and store them in a specific storage solution they sold but I just used pH 7 calibration solution so maybe that was part of the problem. I have read that photographic solutions are hard on some types of sensors, so mine (and yours) may be the wrong type. Could someone recommend a good meter at a good price and some more expertise on how to care for them?