Russ :

FWIW I think what has decreased your visibility is increased plankton growth/bloom. That would be normal in a pond in summer especially where you have had no major rain events and water level is dropping. Aeration could be adding some small amount of visibility reduction. If you do the jar test and use water from the top 3 feet of water in the pond it probably will have some amount of plankton in it. If you take it out of the sunlight for a day or two the plankton will dye and settle to the jar bottom. It will appear as a fine film in the bottom. I hope this helps.