Planted Tank Enthusiast
Join Date: Nov 2006
Location: Calgary, Canada
As a point of reference, a simplified view of saturation is over 250,000 ppm tds(total dissolved solids) or more simply about 25% heavier than distilled water. Most water for human consumption is under 300 ppm tds and our fertilizer additions would do little to change that. So...we're not 'saturating' the water with nutrients....what I think you mean is that we're providing an excess of nutrients when compared to what the plants can absorb or use.
The real issue is that when we put solids into water they dissolve...this means they enter ionic form and are free to combine with a more attractive ion. Think of dry nitrogen fertilizer, KNO3, upon hitting water it become a cation in K+ and an ion, NO3-. This is now aqueous chemistry...the ions are available for reaction within the water and the plants grab what they want.
I guess I'm slowly convincing myself CEC means nothing in an aquarium.