Take a look at Figure 9.
Assume that the nutrient B is Nitrogen, say NO3.
And that nutrient A is CO2 or carbon.

See how a 5ppm NO3 affects the uptake of CO2?
Do you think the demand for CO2 is more critical in that case or at 40ppm?

How about timing of dosing?
Would you have more wiggle room if you dosed say 5x a week at 5ppm or 1x a week?

How about at 40ppm?
1x a week or 5x a week?

You might have excess, but the rate will be more stable for uptake of both A and B.

We do a water change to prevent he build up using EI and virtually every method has some export or has a lower rate of growth(less light/CO2 limitation etc) to manage NO3.

Look at figure 10 and how it affects the other nutrient again.

Look at Figure 11 now.
This one is interesting as the responses to different nutrients, NH4 and K+, produce quite different shaped curves.

How might adding NH4 vs K+ influence plants in our system?
How might excess K+ cause some to believe that their stunted tips are K+ blocking Ca++ when others cannot reproduce the affect when done on purpose in a reference tank?

NH4 is pretty steady going up, K flattens pretty quick.

Finally the last section/figures involves growth trajectories.
These are more real world models.

Through time growth will slow down in many species, but most of the aquatic plants if pruned and kept somewhat constant will keep the high growth rate up.

If you reduce light, obviously the growth rate will slow and the nutrient uptake will slow as well, CO2 demand etc.

Give this a good read.
Then you can go beat up on Amano's claims about algae, or Dupla or whom ever or other folks that make correlation their causation.

Learn and isolate things, test them to see if they are true, do not assume things that often appear to conflict with the observations.

Regards,
Tom Barr