Originally Posted by peckhead
if you invest in a tds meter it will tell you how clean the water is and you will know when to replace your filters by checking your tds when u make fresh ro water. check that bidding site
This won't help him.
Everything a sediment prefilter removes from the water the RO membrane will remove also. The sediment prefilter is there to protect the RO membrane from the easy to catch stuff, because that is also the stuff that will reduce it's life the fastest. It's a cheap filter protecting a very expensive one. Even if you remove a sediment prefilter, the TDS of the product water won't change because the RO membrane is still removing everything that the missing filter was taking out, however the membrane's life will be severely cut down. Long story short, TDS meters test the performance of the entire system, not just one cartridge.
If you rely on a TDS meter to tell you when to replace your prefilter, you'll go thorugh a lot more expensive membranes than necessary. That's why cartridge canisters are often clear... for visual interpretation.