KayEllen@Pheebe Originally i had considered a single proper level sensor like this vs the dumb binary detection scheme I went with, was worried about cost, pit space & reliability, but you bringing up corrosion, over a decade that really could factor in alot. Plus with a proper sensor I can do things like monitor rate of level change vs pump current, and flag if any issues start to occur, like mild clogging or pump wear etc!
PheebeUK@KayEllen having a bit more info often seems to be a good thing. I wonder if you could use a capacitive sense library for your favourite microcontroller to measure the changes. I know the ESP32 has some dedicated hardware for touch that translates increasing capacitance into a reducing count. See https://maakbaas.com/esp32-soil-moisture-sensor/logs/testing-the-sensor/ for an example usage.