MT - you shamed me into it. An update was made today.

Thank you Ray for your fast response.

Another question trots me in the brain!

Can we say that the solution in contact with the roots contains really 125 ppm of nitrogen at every moments? A few days after watering, have we a more concentrate solution at the bottom than at the top? Have we a NPK gradient of concentration from bottom to top?

I do not think the solution stays at 125 ppm N Intruder, as the plant is extracting nutrients from the solution (and increasing that of the waste products). Concerning the gradient issue, consider this:

If anything, the nutrient concentration would be greater not at the bottom, but higher in the medium, as that is where the majority of the evaporation occurs. (Proof for that is the fact that the top surface is where we see the precipitation of minerals.)

However, were are talking about a pretty dilute solution to start with, and nature abhors gradients, so as the water evaporates, the solution will try to stay uniform throughout.

All in all, the nutrient concentration is probably less of a concern that the build-up of waste products.

Thank you All on My Original thread question.
I will water before they dry out then.
thank you's!