This is the fourth season using a SWG. Yesterday I started to fill up the pool. Intex 18' x 48". When there was about 500-600 gallons in it, I started to add salt. The salt I had was left over from last year and the bag was not sealed. The bag sat in my shed over the winter. Can the salt change in a way that would cause the water to change yellow? I would greatly appreciate any help.