Water Testing Question

I have a TDS-3 tester. It’s used to test water for total dissolved solids (hence the TDS) and I use it to check up on my Brita pitchers, among other things. To calibrate it the company offers a calibration fluid of a known concentration. I’m pretty sure it’s a saline solution of a known concentration of NaCl. They offer two concentrations: 342 ppm and 1000 ppm.

I ordered it and received the 1000 ppm. What I wanted was the 342 ppm (not sure whether they or I screwed up – not important). My tester is supposed to be calibrated against the 342, not the 1000.

Here’s my question: Does it make sense to dilute the 1000 ppm solution to, say, one third, and then I would have 333 ppm solution? This would be fine for calibrating if this is rational. It’s not worth it to send the stuff back. It’s not very expensive and shipping is almost as much as the stuff itself.

What do you plan to dilute it with? You’d have to have something with a known TDS of zero.

Well, that was stupid of me. I meant to mention that I propose to use distilled water. Which I assume to have a TDS of zero.

Really, he can dillute anything with a known TDS below 342 ppm. If you’ve got water somewhere with a known TDS of (say) 200 ppm, you can calculate the amount of 1000 ppm stuff to get a final concentration around 342 ppm. Of course that has to be something you’ve measured previously when the device was properly calibrated.

Perhaps grocery store distilled water has TDS close enough to zero for dilluting the 342 ppm solution?

That was my assumption as well, but I really don’t know for sure so I didn’t want to be the one to mention it.

Mixing one part of a solution with 1000 with two parts of distilled water (assume 0 PPM) will not give you a solution of 333 PPM. You will not get a accurate test solution. Part of the 1000 PPM solution is water and the rest is minerals. I remember having to do these calculations in high school chemistry class, do not remember how but it was difficult.

If you want an accurate reading reorder the correct solution.