APPLICATION OF ANALOG SIGNAL ISOLATOR: TWO-IN-ONE WATER QUALITY MONITORING SYSTEM(PH & EC)

Idea Overview
I want to know the water quality of my fish tank. But the water quality instruments are expensive, and they are seems hard to connect with Arduino mainboard. So I want to DIY a water quality system, which can measure the pH value and electric conductivity value.
DFRobot provides variety of water quality sensor. So I want to try doing this simple application, and share it for you.I hope this would help you.

Project equipment
DFRduino UNO R3 (or similar as Arduino UNO R3) x 1
Gravity: IO Expansion Shield for Arduino V7.1 x 1
I2C 16x2 Arduino LCD Display Module(Optional) x 1
Gravity: Analog pH Sensor / Meter Kit For Arduino x 1
Gravity: Analog Electrical Conductivity Sensor / Meter For Arduino x 1
Gravity: Analog Signal Isolator x 1
Wall Adapter Power Supply 7.5VDC 1A (or other power supply) x 1

Making procedure
I want to display the pH value and electric conductivity value on the LCD1602, so I can observe the values anytime. This is convenient for me.
The conductivity sensor sends the small electrical signal into water when measuring, so the electric conductivity sensor will effect the pH sensor when they are in the same liquid. In order to solve this problem, I use the analog signal isolator. This module can isolate the power and signal, so it is suitable for my application to avoid the electronic jamming from the electric conductivity sensor.
One Signal Isolator needs about 75mA electric current. A external power supply, such as 7.5V power, is necessary to ensure the accuracy of arduino's operation voltage.
The usage of the signal isolator is shown as below:

My wiring with the isolator is shown as below:

The connector on the left should be connected to the sensor. The type of the cable is PH2.0-3P to PH2.0-3P.
The connector on the right should be connected to the mainboard, such as arduino. The type of the cable is PH2.0-3P to Dupont-2.54.

prospect
I have some futher ideas to share with you.
The SD card module can be connected to the arduino. The pH value and the electric conductivity value could be recorded. I can load the data from the SD card to do some analysis. 
Some IOT modules can be connected to the arduino, such as WIFI module. Then I could watch the values on my mobile phone at any time. It's very convenient.