I do have some problems reading pH on my setup!
I do not have any EC sensor, but I have a 12V Light Strip controlled with PWM. When I connect the light to the system, it creates erratic pH values. I have changed to a better pH sensor with internal reference, and got better readings. I will try some changes as soon as possible: put a capacitor to filter out the LED PWM output and see if this make any change. I will also try to use an B1205S DC-DC converter with isolation/decoupler. The aim is to isolate the ADS1115 together with the analog signal adapter for BNC sensors.
Here you can see how erratic it becames:
I am running mycodo to monitor a process that starts with pH near 7 and reaches near 8.6 in 4 days.