Spots on leaves in response to K addition?
 

Almost all of my Crypt. wenditii have developed spots on the old growth leaves
that slowly spread until the entire leaf disintegrates. This started the day
after I add Flourish Potassium to my dosing regime. I had also changed the CO2
(yeast based) to a new batch the day before I dosed. Is this something I should
be concerned about or is it a typical crypt "oh my god, something's changed,
drop the leaves, drop the leaves!" reaction to the increased potassium levels?
The other plants in the tank (java ferns and aponogeton) do not have any such
issues and are in fact pearling a bit.

TIA