Low TDS alert occurs when the TDS of the water is below 600ppm and you will notice the OXI OUT has dropped from the default setting of 100%. Ideal TDS levels for the Naked system are between 800-1200ppm. The alert is to warn you that the conductivity of the water has reduced and the system has lost the ability to adequately sanitise the pool.
Most often, low TDS is caused through dilution of the pool water. Other factors can include colder water temperature, not enough flow of water through the cell housing, or a build-up of calcium on the cell plate material where they are not able to produce enough output.
You may also see this alert when starting the system the very first time on a new or renovated pool. If the TDS in the water hasn't had time to circulate throughout the pool, this message will appear however if the water balance is correct the alert will disappear once diluted.
Please refer to the attached Startup Guide which will show how to correctly balance the pool and get the TDS levels back to within range and more than likely salt is required to achieve this.
Add 5-10 kg fo salt in the shallow end of the pool and brush in when the pump is running and allow 30-60 mins for dilution.
More information can be found HERE.