[plantbrain]

EI is a method to address a human, not an aquatic plant issue.
I know folks just will not do it.

The irony is I test a lot myself.
However, I tend not to test like most folks either.
I cannot bet that I'm going to be consistent for more than a short time frame.

So I freeze the water samples and take them to the lab and run them when we run 400 NO3 samples etc. Or I want to know if maintaining at least 50ppm of K+ via K2SO4 will cause any growth issues for a certain species of plant.

So most of the test I do are more to answer a question rather than monitoring.
If you can rely on the test kit's accuracy, then they become useful and you can tweak and modify the dosing routines based on those readings.

However, even so.............what does 10ppm of NO3 really tell you as far as the plants are concerned?

Will 10ppm of NO3 look the same in every tank to all plant species?
Or should we use the plants themselves and consider all the nutrients, and place more weight on CO2 and light intensity and duration?

These are subjective arbitrary choices we make, some are good, but some can be bad. Be careful in seeking more than is really there and that will answer the question/s you may have.

Regards,
Tom Barr