Maybe a little mind shift for you on brix.
Consider sampling sap from a petiole or stem, not the fruit:
"CO2 is free, too. If a plant photosynthesizes faster it’s going to have higher sugar content and a higher Brix level. Once Brix gets over 12, the plant is largely resistant to insects and pathogens. High-Brix plants have formed relationships with soil microbes that are able to supply trace elements and other nutrients that the plant needs for self-defense, for its immune system."
Lub, read this when you get a chance. it expands on a discussion we had on your other thread. Great thoughts on the interaction of roots with soils and microbes. Explains how this interaction is all driven by carbon (simple SUGARS), and why you may consider the brix levels of the plants themselves to explain what is going on rather than just sampling the fruit.
https://www.ecofarmingdaily.com/inte...althy-topsoil/