Not sure about ounces and gallons, but the percentage of salt is the percentage of the total weight of the solution. So, 23 grams of salt in 77 grams of water, is a 23% solution (the solution will be 100g). This makes it easy as 1 ml of water = 1 g. So 230grams in 770 ml of water is 23%. That converts to 298.7 g of salt to a litre. There are 3.79 litres in a US gallon, so that's 1130.7 1130.7 g of salt to a US gallon, which is just under 2.5 lbs of salt (2.487) to a US gallon.