Here's my experience. The bottle tests showed I needed approx a ton of gypsum to clear up my very turbid 1.8 acre pond (2-3 " visibility). I added over 2 tons this spring (over about 6 weeks) with very little to show for it. We had heavy rains over the course of the spring which certainly didn't help me. I talked it over with Clint at Overton and he told me it might take as much as 8 tons. I was putting the gypsum in 1 shovel full at a time in my trolling motor propowash and it was the expensive powedered variety ($10 for a 40# bag but more surface area should be better) so I was pretty discouraged.

The rain slowed way down. I was adding a couple bags of gypsum a day after work and suddenly the pond started to clear. Over the course of a week I went from 4" to 22" of visibility. I also note that there is a similar sized pond downstream of mine that catches the overflow off my pond. That pond cleared first and has 30+" of visibility now. I have fertilized my pond and I am trying to keep it at about 18" of visibility.