TDS meter question

[hammcd]

I am about to order a TDS meter. I saw lots of good reviews for the in-line ones that attach right to your RO/DI. This is super convenient but are the hanfheld ones good as well. I think i'd like to be able to test the water in the ATO container etc. Is there a benefit of one over the other?

These are the 2 im looking at:

in-line - http://www.marinedepot.com/ps_ViewItem.aspx?idproduct=RO1312&idCartRow=28294676&isKit=0">http://www.marinedepot.com/ps_ViewItem.aspx?idproduct=RO1312&idCartRow=28294676&isKit=0</a>

[B]handheld[/B] - [IMG]http://www.marinedepot.com/ps_ViewItem.aspx?idproduct=HB00017&idCartRow=28295924&isKit=0">http://www.marinedepot.com/ps_ViewItem.aspx?idproduct=HB00017&idCartRow=28295924&isKit=0</a>

 

[schwaggs]

I have that very same inline unit and a Hanna handheld unit. IME, I have a hard time trusting either too much as they are tricky to get calibrated. So as long as all you wish to do is measure relative TDS, they are great. I tried calibrating them with calibration fluid but the problem is you are calibrating them a a range that is very far from where you are measuring so you end up with bad results. For example. I calibrated with 342 PPM TDS solution (WAY off from 0-2 that we wish to measure) and when I connected it to my RO output, it read 0 which I know is wrong.

So what I ended up doing is I connected it to my RODI output with a known good DI cartridge, adjusted it to just read 0 (just a hair if a turn so it reads 0) and connected it back up to my RO output and it read 2 PPM. Sounds reasonable... Do I believe my RO output is actually 2? Not really. Do I care if it is 2 or 3 or 1? Not really. All I want to know is when it is 20, or 40 so this pseudo calibration is just fine with me... The other probe is connected after my DI stage and it always reads 0 (even after the DI resin has changed colors), another reason why I don't totally trust them.

If you are serious about reading TDS accurately, you can use the Apex Conductivity probe. It can measure to the fraction of a TDS unit.

 

[hammcd]

hmm i really just wanted it to tell me when to change my RO/DI filters and occasionally the tds of my ATO container water

 

[jennm]

Your container (as discussed by PM) will pick up dust and bacterial film, which is normal and nothing to fret about, but it will skew the TDS readings.

Best test is to collect a sample while the RO is running, into a clean container, or use an in-line.

Jenn

 

[schwaggs]

JennM;694541 wrote: Your container (as discussed by PM) will pick up dust and bacterial film, which is normal and nothing to fret about, but it will skew the TDS readings.

I agree with this completly. I never had much luck measuring TDS in a containter. In fact, when using the handheld unit, the first several readings are always high and each time I empty the cup and re-measure, the reading drops. You have to repeat this several times before getting an accurate reading...