Hi Corey, you have lots of great questions. It’s my understanding that CEC as measured in the lab is the capacity to hold nutrients, not what’s actually being held, so there is really no way to increase it by adding fertility. It’s an inherent property of the soil (an indicator of how much clay and organic matter you have) and the only way to increase it is by increasing the OM level.

Regarding your observations with potassium, what form are you adding? The K2O most commonly used isn’t particularly friendly to soil biology. It’s a strong salt and the chloride that comes with it can bond with calcium and leach out of the profile as calcium chloride, which is highly soluble. Check out this paper on the potassium paradox, which might explain some of what you are seeing: https://www.researchgate.net/publication/262804294_The_potassium_paradox_Implications_for_soil_fertility_crop_production_and_human_health

Cheers