Then I would go with 2.5g/gallon of the Orchid Mix (12.5g/5gallon) and feed that amount so that the roots are using it for about 10 days (however many waterings that is), and then go back to straight MC. Water to runoff with this new stuff.
Then you can go back to the MC and the pH should be back in line.
Then you can go back to the MC and the pH should be back in line.