The lion fish at the zoo requires 456 gallon tank to be 4% salt . Some of the water evaporates raising the salinity to 7% . How much water need to be added to bring the salinity back to 4%

Question

The lion fish at the zoo requires 456 gallon tank to be 4% salt . Some of the water evaporates raising the salinity to 7% . How much water need to be added to bring the salinity back to 4%

Answer 1

Let's look at this on a mass basis. Let S = lbs of salt in a 4% mix with 456 gallons of water

Let W = lbs of water

Then; 456 gallons of water x 8.3417 lbs/gallon = 3803.8 lbs W

For a 4% salinity, S/(S + 3803.8W) = .04 or S = 158.5 lbs Salt

For a 7% salinity, 1583.5S/(158.5S + x lbsW) = .07 or W = 2105.8 lbs W

2105.8 lbs W/8.3417 lbs/gallon = 252.44 gallons W

456 - 252.44 = 203.6 gallons of Water that needs to be added back to the tank for a 4% salinity