Do these TDS reading sound right?

Wow, thanks for the great post AzDesertRat, much appreciated!

I do have a hand held DS meter as well (CD97 made by Milwaukee). It reads the tap water as about 190ppm. The RO membrane is only one year old, so fairly new, but as you say, it seems to be doing it's job!

Thanks for clearing up the confusion on the DI beads releasing contaminants after they are spent. When I hooked up the TDS meter, I positioned the DI housing so it was vertical (I previously had it horizontal on top of the RO membrane housing). It's now much easier to see the beads and I don't know if it's my imagination or not, but it looks like the lighter color spent beads rise/float to the top of the canister, and the darker green beads stay near the bottom. Looks like about half the beads are honey color, and the other half are green. It seems to work much better this way.

 

Just curious, what does your handheld read from water coming from the RO unit before and after the DI? Can you take a water sample and test it? Just curious to find out what the discrepancy between the inline and the handheld might be....

 

I can't easily get a reading going into the DI unit, but both the in line and the hand held read 2ppm out from the DI.

 

Actually what is happening is the cation and anion resins are seperating which is not good. Your DI canister should be packed so tightly the resin does not move. Fill it as full as you can, then tap it on the table top or counter to pack the beads, fill again and repeat until no more can possibly fit. When resins seperate they can actually mess with the pH of the treated water and cause problems. You want it well mixed unless you have special water conditions that require otherwise.

To check your RO only TDS with the handheld, disconect the line from the RO leading to the DI and fill a small clear glass drinking water glass which has been cleaned by hand in very hot water and with absolutely no water spots or soap residue in it. I test with my handheld frequently and the readings never agree with the inlines so I use the inlines as a rough guide only. You also need to make sure the inline probes are rotated in the correct position, they have an arrow or indicator on them that needs to be in the correct position or they won't read correctly.
I would compare all the readings between the handheld and inline and judge for yourself. Even if its off, as long as it is consistent you have an idea where you are.

 

A TDS reading of 2 means its time to replace the DI resin. Don't wait as it is releasing weakly ionized substances already.

 

OK, thanks for that.

It's been about six months since I replaced the DI beads. When I did it, I packed them as tight as I could, and did as you suggest, turning it up and banging it on the table to pack them in there. I guess once it fills up with water it loosens them up somewhat.

I'll replace them tomorrow and get them good and tight!

 

DI resin actually shrinks with time, thats one reason the better vertical 20 oz refillable DI cartridges have sponge inserts in them so they can expand and keep things tight.

 

If mine doesn't have a sponge insert, is this something I can add myself?

I noticed the OUT (from the DI beads) ppm reading once the system was producing water was 0 (not 2 like I said before, not sure why it would make a difference if water is flowing or not). So maybe the beads are still OK, or since they have separated, should I just go ahead and replace them?

 

Inline meters do not work if water is not flowing past the prongs on the probe. You cannot rely on a static or non flowing reading nor can you stick it in a glass of water and get an accurate reading. Thats another drawback. The probes need to be inserted in the tees all the way and rotaed in the correct orientation. If your flowing reading is still 0 then you are OK but mix up your resin, adding more to it and pack it tightly. You could probably add a piece of foam like comes in a phosban reactor or cut up a piece of filter foam.

 

I do have the prongs inserted all the way and orientated in the fitting the correct way, so it should be reading OK.

Thanks for the help and advice...much appreciated... :thumb_up: