Sustain The World Blog Post:
1. Measure Climate Change with Hydroponic System Blog #1 | Concept Design and Plans
2. Measure Climate Change with Hydroponic System Blog #2 | XMC4200 Bring-up and Hydroponic System
4. Measure Climate Change with Hydroponic System Blog #4 | Sunlight Sensor and Water Purity
5. Measure Climate Change with Hydroponic System Blog #5 | Air Flow and CO2 Measurement
Highlights:
Now, almost all sensors that I wanted to use originally are hooked to the XMC4700 Relax kit. For photosynthesis, three parts are important: light, water, and air. For the rest of challenge, I would like to focus on these three parts by taking measurements with the smart hydroponic system, This week, I am focusing on hydroponic water quality including nutrient.
Infineon DC Motor controller shield TLE941112EL is taking a great role of controlling the cooling fan speed and air pump motor.
The air pump motor is important for two things.
1. Add oxygen to roots in hydroponic system
2. Keep nutrient circulate in water, so the water with nutrient is maintained clean.
The picture below is the smart hydroponic system to measure the hydroponic environment.
Water Quality by eye observations
Without water pump. This example below is following the Kratky hydroponic method. The water with nutrient looks bad 
With water pump
TDS value is ~70 ppm if the air pump is running.
pH of water
Most plants like water with pH = ~6.0. So, I usually use 1 gallon bottle. The regular water in my town is about neutral, so I add nutrient and if pH is far from 6.0 then I add pH up or down solution.
Next Steps:
Next, I would like to check air quality in the real system. Also, I would like to update the water quality over time.