Skoag. please make sure your calculations are correct( I did mine wrong first time). 4 tablespoons Alum = 120lbs Alum per acre foot of water. First, is 4 tablespoons the "least" amount of Alum to clear in 12 hours ? Secondly, make sure you add the tablespoon amount you are testing to one gallon of tap water, then add one tablespoon of that mixture to the pond water! If your pond has an average depth of say,5 feet, then you will need to multiply the amount of Alum per acre(either 30, 60, 90, or 120lbs) X 5 acre feet of water.. Please, other members audit my calculations. I don't think your water sample results should interfere with Alum use, but using some hydrated lime is cheap to offset Alum's acidity. There is a good thread addressing these issues under Muddy Water on this forum.