Would you change your filters and resin, if noit only your RO/DI still read 0, but your RO tap on the sink also reads 0 tds? I was considering it, and already have the replacements, but 0 tds? I"m having NO water quality issues, none at all. And as I said, I"m still reading 0 tds after 2 years. My tap runs about 145 TDS fairly consistently. I have a $100, 5 stage system with the drinking water side also- got off Ebay. Water General Manufacturing Co. Also- my DI cannister was remounted to a vertical position, with the flow flowing from bottom to top- and the cannister is clear plastic, so as I can see the 'spent' part which is a browish, and the 'unspent' part whick is purpleish on the bottom. The resin in the clear cannister still has about 2/5'ths unspent. Now I have heard- 'oh, the bacteria will build up in the system after a year.' Why would it? Why a year- I think maybe that was a good interval to change things- but opps, I missed that. Also, I hear of people changing things when there DI reads 1 TDS. OK, so it's starting to get a little spent. BUT, lets say you started with the low # of 5 TDS. Are you aware that after you add the salt mix- it's over 1.000 TDS? I checked my DT- off the scale past 999tds. % wise speaking, how catastrophic would it be to use even as high as 5 TDS before you mix in the salt? Is the 5 TDS purely nitrate and Phos? I doubt it. I just feel some things are taken beyond the extreme in this hobby. I still love my DT and the hobby in general.