"What would be the cause of the history of pond only developing the problem a few years ago?"

I figure the Extremely large grass carp and big channel catfish stirring up the colloidal clay and particles.

"I wouldn't think the soil is much different than before. It might be good to explore this line of thought."

Nope but colloidal clay has a negative charge, bounces off other particles and stays in suspension for a very long time unless something is introduced to cause them to flocculate and drop.

"Early on, was there a treatment that affected water chemistry?"

No, nothing that I am aware of but the pond is fed by a perched water table as well as the surface water.

" One thought, maybe it lost its earlier alkalinity over the years and the recent liming will help ... given time. "

The alkalinity was running at 50 ppm before I added any additional lime. But, as you mentioned, the 800 lb last fall and the 800 lb ag lime earlier this spring may help given time. The alkalinity is now running up between 60 - 70 ppm, calcium hardness the same. Total dissolved solids and Electrical conductivity is also up.

"Another thought, maybe mechanical disturbance is worse than thought, eg maybe other species that OP isn't aware of? Yet this wouldn't explain two weeks and a jar not settling."

Yep, I just got in touch with my neighbors who like to catfish to see if they will come up and get the one channel cat that remains in the pond. Many don't think it would be causing the muddy water but it is big and my pond is very small.

Also, the clay here is intense and seems like it may have the high potential for colloidal particles so it isn't surprising that it isn't settling, especially since I probably didn't use enough alum, or in a proper full treatment to drop it all out yet.

So, now the plan is to get the remaining big catfish out then go at it again with more alum and hydrated lime.

I'll keep this post up-dated.

thanks for your interest and input!

Kathy