Dear JB, thank you so much for your comment! To be honest I have no experience yet with the copper wires for a long period of time; the electrodes are exposed to a voltage only for a short period of time per day. Hower there could be a certain corrosion after some time due to oxigen and other elements in the water. You recommendation to alternate the voltage looks like a good idea though, but will require a change of the sketch of course, but that should be easy. Another possibility would be to use stainless steel electrodes instead of copper for instance using stainless steel welding electrodes. I have also considered to build in a calibration function that enables to compute the lower and upper limits and thus compensate for any deterioration of the copper sensor. Pleas let me know your findings after your experiments. This low cost sensor is anyway worth it to be further developed.
Best Regards
Pedro

Hi Eric, excellent inspiring project and so many views and reactions, great!

Thank You!, Good to hear that it can be done on a Mega as well, very useful tip. The stainless steel welding rod is an excellent idea