I went through same thing couple of years ago. Bought a pallet of bentonite for $500. It worked for a month and then wound up having to drain pond. 18 inch clay liner fixed it for now. $500 wasted on bentonite. I used the sprinkle method.

If you ain't gonna fart, why eat the beans?
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RES,HBG,YP,HSB,SMB,CC,and FHM. .seasonal trout.