Changing DI cartridge?

When should I change the DI cartridge? What TDS level output?

 

Anything higher than 0 IMHO.

 

Change it when you first start to see anything other than 0 TDS on a consistent basis. The reason is resin starts releasing weakly ionized substances even before it is exhausted and it can be released in huge gulp at high levels, much higher than the tap wate rlevel was to begin with since it has been accumulating for hundreds of gallons. Some of these weakly ionized substances include phosphates, silicates and nitrates all of which may not register on a hobbyist grade TDS meter at low levels.

 

I am getting a steady 2-3ppm, change it out?

 

yes. if you normally read 0 ppm its change out time.

 

Yes, it is past due.

 

how do you test for TDS? any kit like po4 or no3 will work?

 

buy a TDS water meter.. they sell them to plumb inline with your ro/di unit or buy a handheld one.. ebay has some.

 

You need a TDS meter, they start around $20. A good entry level meter is the TDS-3 from HM Digital, it is temperature compensated, reads both water temperature and TDS and has a 2% +/- accuracy. Inline meters are OK as indicators but do not have the accuracy of handhelds and you lose the portability since they are dedicated to only two points and cannot be used portable. To test an RO/DI system you need to know 3 TDS readings so it would require two dual inline meters to accomplish.

TDS meters can be found at any of the online RO/DI vendors, on ebay or the Lowes close to me even carries them. www.buckeyefieldsupply.com is a master distributor for HM Digital so carry their full line.

They are the only accurate way to test RO/DI water purity short of lab type instruments like a conductivity or resistivity meter. Color changing DI resins give you a ballpark but are not accurate nor reliable.

 

I have a hand held meter, my tap water runs about 650TDS and I am currently getting 2 or 3 from the RODI system