To ME, first of all it's not an excess of anything but rather a deficiency... and I'd be willing to bet it IS potassium ... which leads me to think your PH is not in a good range so that's the first thing I would check... Potassium is absorbed best in soil at a pH level of 6.0-6.5 (it's different for soiless). I would shoot for a PH of 6.2 so you don't run into issues with any other nutrients. Do you check the PH of your runoff? If you don't, you need to do so as you might have some lockout issues and need to do a flush if the PH of the runoff is badly out of whack (and then get back to your normal water/feed schedule) ... If you don't have a PH pen, the best advice I can give to ANY grower is to invest in one - having the ability to balance the PH accurately wards off many, MANY grow issues and resolves issues that DO crop up.
Good luck!