RBC,
Go to these two sites that do a good job of explaining the use of Aluminum sulfate (alum). One of the sites also discusses the use of Gypsum and how to test to see how much you need of either one of these two compounds.
http://agfacts.tamu.edu/D11/Calhoun/Mar/Recfish/Pondmgt/mudpond.htm http://www.perigee.net/~jrjohns/aluma.html As is explained on the first site there is a specific jar test to do to determine how much alum you need. Alum is harmless to your fish by itself. The danger is too much or too quick of a PH drop if your alkalinity is not high enough to buffer the Alum which is acidic.
The alum for just over $11.00 was not in 100 lb. bags it was 50 lb. bags. Still much better than ordering it!
Last time I used alum I made a "slurry" (mixed pond water and the alum in a plastic garbage cans) out of it and broadcast it over the small 1/10th acre pond via a plastic lemonade pitcher. However the pond I want to use it on now is .62 acres and requires about 300 lbs. I may broadcast the dry crystals on a calm day instead of mixing the slurry as it will be a lot of mixing for a pond this size. I was told by an extension agent I can spread the crystals on a calm day. Not sure if I will as I am skeptical of this but it's an option.
