How many TDS meters do I need for 4-stage RODI?

[ralphie16]

I have a 4 stage RODI system made by Kent Marine. I have a dual inline TDS meter by HM that I have monitoring the water coming from the tap and the water leaving the RODI system. I would like more control over when I have to replace my filters. The manufacturer has some guidelines but I would like to read the TDS going into each filter and coming out so that I can see how each filter degrades over time. So do I hook up each meter to the input and output of each stage and just monitor the TDS change from one week to the next? Does this seem logical and worthwhile to do?

The HM inline tds meter are only like $25 on ebay and I would only need 3, but could get away with 2 even.

[AZDesertRat]

A TDS meter will be of little use in determining when to change prefilters and carbons as they have very little effect on TDS. Prefilters are designed to trap suspended solids not disolved solids and carbons remove chlorine and volatiles. Install your inline after the RO membrane and after the combined RO/DI for best results. That way you can tell when the RO TDS is rising and the membrane needs changing and when your DI resin is shot and in need of replacement.

[RicGio]

Yup, AZDesert rat nailed it.