Dabbling

I just installed a DuPont under sink water filter. It's a single stage with a carbon block filter and it came with its own faucet. Per the instructions I ran 5 gallons of water through the filter before using. I purchased a TDS meter and tested the water straight from the tap it was reading 120 and from the filter its was reading 155. I re-calibrated the meter and the results were similar. I returned the meter thinking its defective. New meter same thing. Returned the second meter and purchased a different brand for more money. Same results. Ran another 10 gal trough the filter no change. Tap reads between107 - 120 and filtered reads 140-155. Does this make sense?