I have a Captive Purity ro/di filter, and for some reason my tds readings are strange. After the tfc, sediment, and carbon filters my tds reads 005. Then after the DI cartridge my tds reads 014. I have the dual in-line tds meter from marine depot. Is my DI resin leaking something that is adding to the tds? Is this even possible? All 3 filters plus the tfc membrane were replaced 4 mos ago, and the tds meter is 3 mos old. Thanks.