Bill D, if his pH was 8.28 in the evening, what would it be mid-day when it is at it's highest reading in the pond?
In my pond, the PH varies very little with time of day. I suspect the high alkalinity acts as a buffer that keeps PH pretty stable but I'm not a chemist. Hopefully, some other folks with experience with this kind of water will chime in.
Bill, remember that the key component to growing fish in a pond is good water quality. Fish don't grow as well when they are stressed, and that "stress" can be a myriad of things. Predators, turbidity, water chemistry, etc. Fish blood has an average pH of 7.4. The closer that the water quality mimics that pH the less stress the fish will be under.
If I was measuring pH in my pond in early morning or late afternoon, with alkalinity in the 150-200+ range, I would want my pH to be in the 7.0 - 7.4 range, but closer to 7.0. That way the daily pH swings will be closer to matching the fish's' pH. To adjust the pH in 870's pond, I would carefully add alum and continually test the pH while doing so. Why alum? It will do two things, drop the pH and bind up excess P that is in the pond. Binding up the excess P will help reduce FA production, which is a problem in his pond.
