pH is the measure of acidity of lake water; 7 is neutral, and values below that are acidic. Every unit drop is a ten-fold difference (remember learning logarithms in school? This is why the numbers are small, and it is also why the p is lower case and H is upper case).
As the pH of White Lake's primary source water--rainfall--has changed, so too has the pH of the lake water. The "new normal" pH is around 6.5, with excursions above that during periods of an algae bloom or when there are high amounts of aquatic vegetation growing on the lake bottom.
Elevated pH levels--above 7 to 7.5 for a sustained period--have not been seen since the alum treatment in early May 2018.