About 2.2 pounds of salt in a cubic foot of sea water. There are about 7.48 gallons in a cubic foot and sea water weighs about 8.5 pounds per gallon (63.58 pounds). Sea water is about 3.5 % salt (usually reported as 35 ppt or parts per thousand). So 63.58 x .035 = 2.2 pounds of salt.
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