Just tossing the powder doesnt work well. It's best used when tilled with soil then watered immediately so it swells. It's basically a clay powder. Last quote to dig out our tank and add clay was $1500 for dozer not including trucking for clay. Never priced a bentonite truck but highly unlikely it was that high and could be done in about 2 hours. Instead, the neighbor has a cat 320 excavator, not to mention it had already accumulated 3 foot from recent rains. Chose to dig from a dried up 8' to 20' then slope one side for the cows. Knocked out a burn that diverted alot of runoff. With last few rains its full(+-3/4ac pond).

I’ve tried by mixing several times.

If you do it I have a pump for you, brand new still in the box - https://www.amazon.com/Pentair-DS3HG-01-Single-Phase-Priming-Centrifugal/dp/B006H3ZODC

There is 43,560 cubic feet in an acre foot of water and 7.38 gallons in a cubic foot.

43,560 X 7.48 X 4= 1,303,315 gallons not counting the deeper part.

Gone suck up the electricity