Brian K, you can buy a small test jar of it in the spice section of Walmart, etc. For amounts that are needed in the pond, you need to go to a chemical supplier like Helena Chemical or a place that sells farm fertilizer. Thats's where I get mine. McCormick Alum

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).