Once again, thanks so much for all the important information Bob! I’ve never done a night time pH measurement but that would be interesting. We also tested for Nitrate when we got this pH result, it was .093 mg/l. The pH measurement and N03 sample were taken at 1230 pm.
The time of day is important because a high pH can be caused by the presence of algae. Do you have night time pH measurements? If night time pH measurements are low then it might speak to a phosphorous problem. If they fluctuate throughout the week and are not diurnal then the likely cause is to be found in the storm drains. I have seen run off of alkaline cleanser from commercial activities in Occidental. I would look to activities such as the outside washing of floor mats from restaurants and such things. Do you have nitrogen measurements or grease and oil measurements?