My pool is 15 years old. Every season I add approx. 500 lbs of salt to raise my salt level to 4500 ppm. This year i have had to add 1200 lbs of salt to attain 4500 ppm. I used Sifto pool salt for this. Now my pool is extremely salty and just not as pleasant to be in. Is it possible to get bad salt? Any ideas would appreciated.