I have an old pond on my place that doesn't hold water. The soil is sand on top, with clay about 8' down under the sand. It is not spring fed, just catches runoff from heavy rains. Next year, I plan to dig it out a little more and clean it up. Then I will run a water line from my well over to the pond to keep it full. But it needs to be sealed to hold water. I was thinking bentonite, but also looking at soilfloc. I'll be able to apply whichever I choose to a dry pond bottom. It looks like soilfloc might be cheaper than bentonite per sf. Is that correct? Can it be applied dry, or does it need water in the pond first?

Also, my biggest question about soilfloc is potential toxicity. If I eat fish from the pond, will they have microplastics or polymers in them from the soilfloc? Even if it doesn't kill the fish, I don't want to eat it.

Is there something other than bentonite or soilfloc that I should consider using in the sand?

Thanks for your help!