All your tests are dynamic readings that will change throughout the day. Dissolved oxygen and ammonia will peak in the late afternoon/early evening. One test in the morning really doesn't lend any insight. Tests should be conducted in the early morning, mid day and early evening on the same day, twice per month. Since you are just starting out, I would recommend at least once per week. Always record the conditions of the test. Atmospheric temperature, high/low pressure, sun/cloudy, etc. The more parameters documented, the more insight you will glean.
Since you have relatively low plant life but decent secchi readings, I have to ask how often you treat your pond with copper sulfate or other weed control chemicals?
I don't have any insight as to whether your pond is overstocked but I'll assume you are feeding? This could be over feeding? The higher protein of your feed, coupled with over feeding, I would expect to see the results you posted.
I don't think ammonia is an issue, currently, considering your temp and pH. However, you should try other ways to increase DO. Maybe a water fountain or spray? Anything to increase the waters interaction with the atmosphere.
Mike Whatley has a photo of a pump he used to increase DO, he may have some insight into its efficacy?
