ph. swings widely on a diurnal basis. Alkalinity is the measure to note, At 24 pre lime you have a base to work from. It is low but manageable if you don't have high water turnover (flow) through the pond. Lime applications have a small initial effect (a few ppm increase) followed by a longer term bell curve result. Alkalinity will jump a few points to start and continue to clime for a period of mths to a couple years and then start a slow decline. The shape and duration of the curve will depend on how much lime you put in and the condition of the water.