I was looking around on the computer and some things popped up in the ads (no not pornhub lmao) and got me thinking...
The Hanna Instruments HI83325 is a compact, multiparameter photometer with digital pH electrode input for use in plant nutrient analysis.
www.hannainst.com
The HI96752 portable photometer uses an adaptation of the oxalate method for calcium and an adaptation of the calmagite method for magnesium measurement.
www.hannainst.com
Got me thinking how cool these tools and others like them (I didn't look long) would be especially for those running large recirculating hydro systems. I know the pros do this in their commercial gardens allowing them to simply add back what element/s are lacking instead of dumping all the time.
So you get a solid analysis on what the plants like for feed at any point in their cycle, make that your baseline elemental PPM's. You can test the nutrients regularly and see what elements are being consumed and at what rates, then you can address the shortages without adding excess in other areas.
You can also tune your feed to what the plant is really pulling out of the nutrient solution.
You could chart the elemental consumption over time and if you run into a condition that is favorable you can see exactly what it was that changed.
This is something I will have to put on my wish list and play with when I have more time.