So I've been working on a project for my fishtank. In the fishtank there is a temperature sensor and a pH sensor. These are connected to an arduino Uno WiFi board along with an RTC module, SSR and a nextion display. The following is connected to the SSR: lights, heater, pump (all for the fishtank).
When I'm measuring the pH in the calibration liquid, or any other liquid at all, I'm receiving stable readings. When I put the pH sensor in the fish tank and turn anything on (lights, heater or pump), the measurements starts to go up and down and isn't stable anymore. In the circuit there is also a 100 uF and 100 pF capacitor. Am I missing something or is there a way to prevent this from happening?