For every 1000 ppm increase in salinity level, you need to add 0.5 bags of salt to 10000 liters of water. In case your pool contains 20,000 liters, you need to add one full salt bag
Swimming pool salt 50kg
Salt is not an alternative to chlorine. Salt is added to a pool so that it can be used with a chlorine generator which generates chlorine from the salt. This is the same method that chemical companies use to make liquid chlorine. Some people like the feel of salt in pool water.