Pottasium has problems uptaking at lower ph, it uptakes best at 7-7.5
although 0.8 may seem like minute 1 standard deviation from 6-7 is 10x, PH is logarithmic like earthquakes, and 6 is 10x the acidity of 7.
We base water as the universal solvent it sits distilled at room temperature ph 7 @ 24 degrees
The same water at 100 degrees is 6.2ph, that 0.8 difference, which makes it 8x more acidic.
In my humble opinion at this stage, your ph should be at 7.
Apply pottasium in foliar spray for quick solution in meantime.