I have an old fish tank that I'm repuposing as a fish tank. I have to use tap water that is quite chlorinated. I have no idea how many gallons came through the hose and I must use a de-chlorinating solution that says use a teaspoon for every 10 gallons. The tank is: 16"h x 24"l x 12"w. Can any one give me the formula for converting cubic inches to gallons of water? Thank you and the fish thank you.