Five Years now with our present setup for Filtering the Water, Hardness & Iron Content are part of the Rural Landscape if you will.. We have a HD Water Softener and use the Rust Remover Salt with a Resin Dispenser.. Plus a 7 Stage Reverse Osmosis Filtering system tied into the kitchen Cold Water.. Now here's my Query, upon installation we were told the 3 main large filters are to be changed yearly and we have followed that advice.. With the 4 remaining Filters to be changed out every 5 years.. This time around calls for all 7 filters to be done at the sametime, Tech comes and with his Pocket Sized TDS Meter and Glass of Water directly from the Kitchen Cold Water (Not RO Tap) reading shows (#9).. Tech says with that Reading Filters are fine for now , maybe in the late Spring Filters will have to be changed and that's all 7.. The (#9) How good is that Reading? I'm surprised that the 3 main Filters at least don't have to be Changed? Opinions Appreciated, Cheers Thanks