Gypsum can clear up water in a few days. Several years ago, Todd Overton and I worked over George's sons 3-4 acre pond with gypsum with large dump trucks from Oklahoma. That's the trick because the OK gypsum was pulverized, and is extremely good at spreading. Some of the pond areas even looked milky later. We cut off surface aeration, and the pond was crystal clear in 2 days.
I had set up a rig with tarps, a tractor with a bucket, and a 2" Honda pump and nozzle. We moved the tarps as we hiphoped by blowing the gypsum off the tarps, and not spreading any mud. It worked great, and we got the whole pond done in a couple of hours.
Having said all that, it doesn't all the time. Esshup or others may figure the gypsum/water percent needed. The results of that may show it doesn't work. The second issue is that most of the gypsum in other locations gets gypsum in bags, and most are pellets. Small but pellets, so they don't spread as well. I use those because of the transport expense, and they kind/sorta work, but not as well as aluminum sulfate. I'm thinking about how to cycle gypsum pellets in an IBC tote until they turn to powder.
