I would be curious the percent of phosphorous in your fish food. Most list it on the labeling somewhere.
Also, try testing your watershed before it reaches your pond. Considering your watershed is pasture (cattle?) they can be a major source of nitrogen and phosphorous. Best if the test is from just after the pasture area.https://www.epa.gov/nutrient-policy-data/estimated-animal-agriculture-nitrogen-and-phosphorus-manure
The best way to prevent turbidity from entering your pond through the watershed is to slow the water down.