How do I know when to change carbon filter, ro membrane, and di cartridge?

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thoeffe

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How do I know when to change carbon filter, ro membrane, and di cartridge? I have a used spectrapure with dual ro membranes in series. I have an inline tds meter. After the dual RO stage it reads 9 and after the DI stage it reads 8. The carbon and sediment filters haven't been changed for quite awhile and are pretty nasty so I'm wondering if that's reducing the ability of the ro and the di stage or if the ro membranes and DI cartridge also need changed. I bought it used.
 
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Uncle99

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You change your membrane when it can no longer remove 90-95% of the source water contaminants. So if your tap water was 100, we expect no more than 5ppm out of the membrane.

You change your DI resin when your final water shows 1ppm or above.

Keep an eye on your membrane output as DI can easily mask its poor performance however you’ll notice that your DI resin is exhausting way quicker than normal.

Carbon and sediment are cheap so every 6-9 months, when the sediment filter starts to turn from white to brown, change it.
 
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