@Abe_Fouhy yes, water and oil viscosity similar?
Cool it is actually less kinematic viscosity at .869 vs 1.0 for distilled water at 20c. @Nedman would polypropylene impellers degrade in mineral oil or would it be fine since it is a polymerization of oil?
@donkjr For me, reading water quality is just a fun function to have. Reading it once per week is probably enough 
Heck, i even control the mirror temps on my machine, to tell me when it´s time to clean them
And, about the mineral oil. I tested it yesterday after a discussion on facebook. The brand i had had about half of the thermal pickup compared to plain distilled water.
I only tested it with a peltier and regulated power and measured the heat, not any data of real use in a tube.
@HP_Persson whoa mirror temps … interesting.
I’m going to “get as close as I can to distilled water by using distilled water”
Mineral oil has a couple of drawbacks in this application. One the thermal capacity about 3.5x less than water and the thermal conductivity is about 2.5x less than water (consistent with @HP_Persson 's results). Second is that the viscosity of mineral oil is about 15X that of water at 20C (this will actually vary as mineral oil can be found in different viscosities). The higher viscosity of mineral oil will mean much higher pressure on the glass which can cause fractures (I’ve crack a glass cooling jacket in the lab before using water because of too much back pressure).
All: some change in our recommendation.
I changed my water last night with the 1oz/5Gal and the conductivity was 281 uS :(.
Not what I expected (<10).
Short story;
… the sources conductivity data is bogus
@Nedman re-calcuated and we should expect in the range of 30uS using .25oz of Clorox in 5 gal. So I suggest this is the currently correct formulation :).
I am going to do some empirical measurements at these concentrations to verify the calcs.
I will update this post as I run more tests. I also plan to restart the long term tests.
Note that the calc I did wasn’t rigorous and I am making some assumptions on the actually ion concentrations based on the MSDS sheet for the bleach (approx 7% NaClO). I suspect the actual conductivity value for 0.25oz bleach into 5gal water is going to be a bit higher than 30us. In fact if we take Don’s value of 281us for 1oz bleach and divide by 4 (should be linear) we get 70us. That’s why Don is going to make a series of solutions and measure with his conductivity meter to verify.
I completed the coolant remix and test. I tested the conductivity at 1x and 1/2x concentration for the needed amount to control algae.
1x = 44.9-46 uS (measure 1/2 at a time)
1/2 x = 22 uS
@Nedman was close…nice.
Conclusion: add 6ml Clorox to 5 gallons of water and your conductivity will run in the 40’s uS.
Yeah for science! 