Very low PK fertilizers. (K-lite)

[Ray]

Plants do not have pumps for all nutrient ions, only certain ones.

That linked study pertained to terrestrial plants, not epiphytes, and there are huge differences between the two.

Most nutritional studies have been done on dicots, not monocots.

In a chart presented in Marschner's Mineral Nutrition in Higher Plants, he shows the content of maize (a monocot) roots after 4 days of exposure to a fertilizer solution. To try to make a table, I'll list the ion, the millimoles in the solution, and the millimoles found in the roots, then in parenthes, the multiplier:

Potassium 2.00 160 (80)
Calcium 1.00 3 (3)
Sodium 0.32 0.6 (1.875)
Phosphate 0.25 6 (24)
Nitrate 2.00 38 (19)
Sulfate 0.67 14 (20.9)

I'll add that you might want to go over to the Slippertalk forum - there are several detailed threads on this subject