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What setting is salt system set for and how often do you use boost function?
Either use your salt test strips to test the salt or bring a sample in to your dealer before blindly adding salt. If your cartridge is only 2 months old and has failed, Hot Spring should compensate your dealer and they would provide you a replacement assuming your water chemistry is decent.
Usually when a salt cartridge fails the display will give you that low salt / inactive reading. When that happens though, adding salt or anything else doesn't make it work again. That is why if you are not at or around that 4 month mark you need an additional way to verify the salt, like the salt test strips that came with the system or your dealer.