The reason behind the high readings is mostly due to the performance of your old salt cell. Older, used salt cells are essentially dying. Its conductivity is minimized giving you “low salt” results on the control unit.
Usually, pool owners will resolve this by adding salt to their water to increase the salinity for correct operation. Eventually the old cell will die and no longer produce chlorine at the rate it should. When this happens, naturally you’ll need to replace the old cell with a brand new cell.
When the new cell is installed, the salinity ends up being higher than it was because you’ve been compensating for the old cell’s lack of chlorine production. When customers see this, a lot of times they’ll go to their local pool store and have them test their water. As this useful post on Trouble Free Pools suggests, pool store salt tests are more likely to be off than your new salt cell’s reading.
To solve this, you can reduce the salinity by back-washing and slowly adding fresh water (2″ increments), bringing you to a normal level once more.
Keep in mind that this happens regardless of the brand you have. Whether it be OEM or generic, this process is possible.
There you have it, folks. Case closed!