I still think your problem may be with the PH
While Nitrogen and Potassium run close to parallel in PH availability, if the PH goes to high (too much fertilizer in your case) then this locks out the Manganese a fair bit which interferes with your Potassium intake.
The leaves don't go yellow, so you automatically don't assume you have a Nitrogen deficiency.
Sometimes it's the trace minerals that are responsible for issues.
Here.... take a look
http://www.eldoradochemical.com/fertiliz1.htm
Chlorinated water was another possible, but I assume you fairly good water?
Cheers Jimmy.