I am doing a mini waste water plant with cascaded PVC tanks (and PVC fittings) for my university project. Each tank has a mixer (the motor is grounded). I made a pH amplification PCB which works with its own battery then send wirelessly the information to my computer.
I was advised that it could be a ground loop, I trace the supposed path on the graphic. Near 1 unit of pH error in the 2nd tank if I compare with a sample taken in a beaker. The error seems proportional to the water flow.
What could be the best approach to solve the issue? Independent PCB for each pH-meter? ground electrodes like stainless steel faraday cages around electrodes connected both together? Or even connected together and with the negative pole of the battery?