This is nothing to do with crosstalk, these are electrolytically in contact with the same solution, so
must be isolated in order to measure anything meaningful. In fact I suspect the entire Arduino system will need to float for truly accuracte measurement.
Given the electrode potentials are unknown I think you need complete isolation with small relays -
any semiconductor approach might not work if one sensor has significantly different electrode potential
from the other (creating an inadvertent elctrochemical cell between the devices)
So I presume you'd need at least s 3PDT relay for GND, power, signal?
Yes the problem is that both sensors are electrolytically in contact with the same solution, so these are the situations where I get right readings: Either I get the sensor out of the solution or I switch off both power and ground.
Im using arduino MEGa and All the sensors are powered from 5v Source (one source) sorry if I didn't mention that( I dont know if that what you mean by electrode potential).
Currently I am not having any schematic for the system, I may handwrite and upload it if it's urgently needed.