An RO system will lower the TDS by 90% depending on the quality of equipment.
Starting with 2800TDS and getting to 500TDS is not bad, but if you are looking for 0 you will need to either up grade to a light commercial unit that can take the that is sized for your set up with pumps or go with another ro system to use the treated and treat it again to get it close to the 0.
It is not an answer to say for drinking, that is the main use for the RO, but what is up with the high starting tds..
Is that tds salt ? sea water?