Morning Hope - hope all is well!
Just a quickie, as you say you have frazzled them a bit, it is no drama in cubes, a flush with a mild mix and back to normal at a lower EC. Flushing with plain water in my mind confuses the plant as one day it has food the other day it can't find any etc...a lower dose washed through until the EC in and out match and you can be safe in the knowledge you have removed all unwanted salts - maybe as they are F&D whilst cleaning the salts out do some top watering just to make sure you remove all excess.
Good shout on a PH pen - the ability to test accurately and regularly is ever so important - it becomes religious, wake up, tea and doobie, check PH and EC, then get up for the day