Q.Why My Bok Choy Plants Started To Rot At The Base And Roots In Hydroponic Garden
My plants were growing great and I was picking off outside leaves as needed then after 5-6 weeks plants started to wilt and rot

Certified GKH Gardening Expert
Yes. Plants do not have an immune system, so it will be up to you to be the immune system. In water, this is even more important. Soil has a beneficial microbe content that cannot be achieved in water. Good practice is key to success in hydroponics. Cycling water is crucial to hydroponic gardening.

Certified GKH Gardening Expert
In a hydroponic setting, these plants will rot at, nearly, any sign of stress. With this being said, the main causes of stress for the plant will be water temperature imbalances, nutrient imbalances, and pH imbalances.
Water needs to remain cool. Anything above 70 degrees will facilitate microbial growth.
Nutrient content will need to remain modest. This means testing and adjusting, daily, to keep the nutrient range between about 500 and 800 ppm. Keep in mind that as water evaporates, or gets used, nutrient ppm will increase dramatically. Keep the water level as constant as possible to avoid . Many times, this will keep the pH stable, but not always.
Keeping the pH around 5.5 to 5.8 will be ideal, here. Doing so will help prevent infections, and keep the plant healthy.
Make sure that the water is changed, at least, once per month or more. Run the roots under fresh water to help remove salt deposits. Then, refill with fresh water and nutrients, testing pH and nutrient content occasionally.
Here are some articles that will offer more information:
https://www.gardeningknowhow.com/garden-how-to/propagation/propgen
https://www.gardeningknowhow.com/special/containers/deep-water-culture-for-plants.htm
https://www.gardeningknowhow.com/special/containers/hydroponic-gardening-indoors.htm
https://www.gardeningknowhow.com/special/containers/basic-hydroponic-equipment.htm
https://www.gardeningknowhow.com/special/containers/hydroponic-water-temperature.htm
https://www.gardeningknowhow.com/edible/vegetables/bok-choy/planting-bok-choy.htm

BushDoctor - Thank you very much for your advice! One more question for you, it isn't very convenient for me to change my reservoir nutrient solution. If I use H2O2 dosing to help keep bad actors away do I still need to change out reservoir ?