I guess it depends on your weather. Dry soils, dry air, etc can be a factor although 1/2” per day seems a bit steep. I wouldnt spend much money on leak theories until you have watched it a few months.

For the suspended clay, the thing that made the most diff for me was ag lime both in the pond and on the surrounding pasture. Then of course soil stabilzation around the pond(straw,grass,etc).

-Jason