Bill...I used 200 lbs in about an 3 acre inches of water. I probably only needed to use 100, but I had it on hand and wanted to be 100% certain before I refilled the pond. I never extrapolated with 100G tank because I knew a few 50 lb bags would be more than enough. It was horrible killing thousands of grass shrimp, fhm, and crayfish. Got all I could save...still it was Armageddon - hard to witness.

Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau

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