I have recently had some turbidity problems with my pond and embarked on the gypsum slurry test described on the Texas A&M website under "Clearing Muddy Ponds". Not having any gypsum handy I went to the neighborhood feed and seed store and bought a 50# sack of pelletized agricultural gypsum. When I made my slurry with 2 tbs of gypsum in a gallon of water it turned cloudier than my pond water by a huge amount. This happened with purified water! Some of the turbidity settled overnight but most stayed. When I used it as a slurry I could not get any clearing of the pond water at any concentration.
I then tried aluminum sulfate which worked like a charm. I assume the turbidity from the gypsum was due to a binding agent used to pelletize gypsum dust but am at a loss to understand why no amount of gypsum I added would clear my water. The only difference between aluminum and calcium is the valence of +3(alum) and +2(calcium). Is there some chemical explanation like the different dissociation constants of the two elements?

Layton Runkle