Salty Dog

I have 15000 gallon pool running a Hayward Aqua-rite AQR15. Over the past 5 years I have add dozens of bags of salt. It seems like every two months it requires two 40lb bags. I have very rarely bleed off excess water and have never added a drop of fresh water. I am in South Florida and we do have frequent rain, but that typically only adds a few inches, then evaporation usually brings the water level back down to normal. Supposedly, salt doesn’t dissipate or evaporate. At this point, my pool should be as salty as the Dead Sea, but it reads 2700. Any thoughts?