Pond Boss Forums GENERAL QUESTIONS Help 5 year old pond never cleared?

I suggest you do an advanced search for "turbidity", particularly in the Questions and Observations forum. One particular result I got doing that which looks informative and correct is this one from the late Todd Overton.

I will also add that my second pond got murky with suspended clay when ever there was a heavy rain; after I added aeration it was cloudy all the time. I cleared that up with a couple of front end loaders full of limestone screenings (a fairly cheap and safe item to try IMHO). It has stayed free of suspended clay ever since. (I add another FEL full of limestone every couple of years.)

There are several more expert than I am on this issue here and hopefully they will chime in.