you need to check your refill rate. It looks like you are flowing a lot more than .5 GPM.
My math is a little rusty on rectangular tanks but here it goes.
14x16=224 cu. inches per inch of height, so 8" would be approximately 1 Cu. Ft, or 7.5 gallons, , you need 4 gallons so you would have approximately 5" of water, times 2 for salt displacement, add 2 inches for the aircheck, you should have approximately 12" of salt in the brine tank.
The picture of your systems is also a good example of why round brine tanks are preferred to square, unless it is pregnant.
Can someone else here recheck my math? I dont have time today to pull my cheat sheets.
You need to remove the tube at the brine tank and measure it in the refill position. Be sure it is flowing at .5 GPM. I am guessing it is exceeding that considerably. Unless my math is totally wrong.