Hi,
Well there are two basic types of uptake mechanisms, and active channel, which means there is a specific protein dedicated to attracting and transporting the target nutrient across the outer cell membrane, and there is the passive channel which normally works through diffusion. Many nutrient uptake pathways have both types of channels. There are even different protein channels that function based on low availability of the nutrient as well as high availability. So the physiology of the plant changes in terms of protein distribution across the leaf based on what nutrients are present in the water and in what concentration. As you mentioned Ca++ only has the single passive diffusion method. As the leaf grows, so does the surface of the leaf, so even given limits of diffusion rates, there is more available contact area for the Ca++ ion to diffuse through. However, once inside the plant there is a system of Ca++ transport within the leaf that is very efficient and very quick. There are transporters located in the vacuole, in the cytoplasm, and in the endoplasmic reticulum. So Ca++ moves around within the leaf very quickly but cannot leave the leaf. Ca++ tends to remain in the leaf and actually builds up to possibly toxic levels because it is also used to modulate the turgidity of cell walls. The problem with Ca++ for plants has far more to do controlling toxicity because of the lack of intra-leaf mobility and the buildup. Calcium failure in the leaf should more likely appear as disintegration of the cell walls, which should more resemble melting or mushiness that deformation, because it part of every cell.
The rate of diffusion of any nutrient across the cell walls always have a pathway. If it's not through a major artery like the xylem/phloem then it will be through some other chemical pathway. Under photonic duress all pathways are stressed, and nutrient delivery of all micronutrients are stifled because they are not very mobile and do not have access to the preferred arterial pathways. That is one reason, for example, that micronutrient deficiency is almost always noted more readily on new growth, because the nutrient has no pathway for redistribution from old leaves to new leaves. On the other hand, Carbon and NPK are extremely mobile, and so failure in these areas tend to characterized by degradation of older leaves first or all leaves simultaneously as the plants attempt to redistribute the nutrient to the new growing leaves.
The problem with carbon failure is that carbon is so important, it is everywhere and in every system in the plant, and so carbon failures take a hundred different shapes from distorted structure to transparency, holes and rotting. Carbon failure look like a lot of different things. But Calcium also has a lot of different appearance depending on the plant because it's used in a variety of ways. It's actually quite rare to see a Calcium deficiency because the usage rate is so small. Also, a lot of the data comes from terrestrial plants and may not apply to aquatics.
There is always a probability that the plant suffers K+ toxicity, however, I get nice growth too and my tanks are always loaded with K+, so what I'm saying is that my observations lead me to believe that it can't be as straightforward as only having too much K+. From a methodology standpoint, my inclination would be first to address the most common cause. As I mentioned, people assume that their CO2 is good just because the DC is green. They automatically assume that the plant needs light, so they set up a situation where the plant fails due to excessive lighting and most times it turns out that it is the Carbon processing that can't get it there in time. People assume that a green dropchecker is automatic evidence of 30ppm, which is not true for the plant. Deep in the plant beds the amount of Aqueous CO2 reaching the leaves is only 10% of what the free water column has. That's why I'm always skeptical of claims that CO2 is good. It happens far more frequently that the hobbyist does not explore the limits of CO2 sufficiently. So that's why I suggest to first remove the light intensity just to see if reduction of PAR (which folks almost never try, let alone talk about) is an easier fix.
Cheers,