Here's a little report about my system...
I bought the
HM Digital COM-100 EC/TDS Meter that Neil suggested from
amazon for ~$60 USD. It's a nice meter -- read the small print manual to learn what and how it does its thing. Once you get the hang of it, it is reasonably easy to use although it has small little buttons closely spaced but a clear easy to read (with glasses) screen I'll take Neil's word that its accuracy is above the typical $15 meter.
The COM-100 has multiple measures for electrical conductivity (EC) in micro and milli-Siemens (µS, mS) and for TDS in pp-million and pp-thousand. There are two ppm/ppt options, One for salt that uses the 0.5 NaCL scale and a proprietary scale named 442(tm) that "simulates the properties of natural water (rivers, lakes, drinking water etc.) witha combination of 40% Sodium Bicarbonate, 40% Sodium Sulfate and 20% Chloride." Apparently an earlier version had a KCl scal for Potassium Chloride but that is no longer included although it is shown in the outdated on-line manual which notes the meter is calibrated with a 1413 µS KCl solution. The meter can be calibrated - I won't get into that, and it has a replaceable sensor.
You click one of the small buttons to rotate through the 6 'modes' described above. I choose to pay attention to the µS micro-Siemens EC reading and the 442 ppm settings. Note the 442 mode is labeled '0.7' on the screen and the NaCL mode is name ''05'. They could have labeled them 442 and NaCL (which the earlier model did) - but someone figured that was too straightforward. No doubt there are reasons for their labeling choices, but heh that's what we amateurs get when we choose to use a 'professional tool'.
Anyway ...
I needed to change the water+solution in my wash tank and also the distilled water in my rinse tank.
I used the each tank's pump to take the old water out. I did not change the filter water on either.
Here is where the fun starts.
With a tankful of fresh grocery store distilled water the COM-100 told me the tank now measued 1
.2 µS conductivity and
0.7ppm for the 442/0.7 mode. Normally I expect distilled water to measure 0.00 ppm - but that was using my old $18 7Pros TDS meter I bought in 2018. Go figure. The grocery store distilled water is steam-distilled which is probably good enough for steam-irons and I'll postulate it's good enough for record cleaning. I used to buy 5 gallon jugs of Nerl Reaent Grade Lab Water - but that got too expensive and the shipping became a killer. Maybe this meter is more accurate !
Next I added Tergitol 15-S-9 in a 0.0150% concentration and, now that Neil is a little more relaxed on IPA, I decided to go back to using that. Or, at least I'll try it until it evaporates over time. I probably don't need the IPA as I had good results from Tergitol alone, but hey, DIY. In all honesty I had a bit higher concentration of Tergitol. 0.0150% in my tank works out to ~1.8ml. I used 2ml and I'll get a wee bit of foam from that and detergency.
With the solution in the wash tank I took another measurement. Now the meter gave a 5.0 µS conductivity and a 3.2 ppm reading on the 0.7 mode. Pretty low by my experience and, being fanatical, another reason to rinse.
Here is where it gets wierd.
I filled my Elma S120 rinse tank with grocery store distilled water. A mix of brands. The COM-100 gave me a 0.7 mode ppm reading of 23.4! I have no clue other than to suspect my grocery store jugs were mis-labeled or mis-distilled or just a lower standard. Horrors - It would seem that my belief all distilled water was pretty much the same was shattered - hah. I'll need to get something different. Maybe I'll take the meter to the store.
I suppose the moral of the story for those who read this far is:
test your water.
... wait a minute. Just before hitting 'reply' I checked and found 2 more jugs of grocery store distilled water under the sink - two different brands. With the 'Food Club' brand the meter gave me a 0.7 ppm. The 'Nature Valley' brand showed 6.7ppm. aha! The moral of the story holds.