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When an AquaRite cell is wearing out, it is common for the salt reading to read lower than actual. Adding extra salt brings the salt level to above normal, allows the cell to read normal, and the SWG to continue operating correctly for a while. Because of this, it is fairly common for the pool to end up with too high a salt level. The new cell reads the high salt level correctly, and refuses to run. If this is what is happening to you, your only option is to replace water to get the salt level down.