Here are the 3 important numbers you need before you start…

1. Final chlorine solution volume = 100 litres = 100,000ml (because 1 litre = 1000ml)

2. Final chlorine solution concentration desired = 200ppm

3. Initial chlorine solution concentration = 12.5% solution = 125,000/1,000,000 which can also be expressed as 125,000 parts per million (ppm) because 1ppm = 1ml in 1,000,000ml ///

1% = 10,000 ppm (10,000 / 1,000,000)