I was considering a 50/50 propylene glycol to distilled water. Or even 100% PG. I’m no chemist, I’m no laser expert. I have worked with a lot of water cooled laboratory test equipment, and I’ve got some concerns about the bleach. I don’t know what it does to the dielectric strength. Maybe thats not important? Assuming the bleach is to prevent things living in the fluid such as bacteria and fungus. The chlorine will evaporate fairly quickly into gas, not in solution with the water. We used propylene glycol because of its low toxicity, and compatibility with the common materials found in lab equipment. And it doesn’t cause rust.
@BeenThere_DoneThat our resident chemist @Nedman has looked at this and we think at this dilution the Clorox it will be an ok additive.
Honestly we do not know the exact failure mechanism but we know it fails at high conductivity. We have had MANY users correct arching noise and reduced power, like you had, by replacing their coolant with distilled water.
The water is insulated from the ionization chamber by the water jacket but apparently if the coolant gets to conductive it will allow an arc (usually around the anode) and draw current from the supply. So the coolant is not breaking down, just conducting. This situation might be different than other lab coolant configurations because of the unusually high voltage and current needed to ionize.
We have plenty of evidence backed by measurements that antifreeze will increase the conductivity 400x and that this conductivity level will cause problems.
So we are recommending that users keep the conductivity of their coolant at levels close to distilled water and change it as often as possible if the levels get elevate. The levels typically get high with algae growth. We do not know what the maximum acceptable levels are but we know that in the 400uS is bad.
We have not measured distilled water and algae-cide yet to see if it is a good formula. That’s another option.
Details and measurements are on my blog post on the subject.
@Bob_Buechler purified water measured 12uS so its 3-4x more conductive but still very low.
I am guessing it would be ok. @Nedman ?
Google distilled vs purified and you get a lot of interesting info. In general distilled is well “distilled” but then often purified as well …heh!
Purified is cheaper cause it is usually purified by reverse osmosis which is cheaper. Go figure…
Went ahead with Distilled. Was able to find an affordable source for it. I found that research, which only added to my confusion, given that they both seemed like they should have roughly comparable uS levels. In the end, I definitely defer to you and Ned on this. 
@Bob_Buechler - my water tank holds about 1 gallon. It’s less than a dollar at the grocery store.
Sorry for my ignorance. The units “uS” is that a “micro siemens”?
How are you measuring that?
I’ve worked with fluid resistivity meters before, but not those units.
@BeenThere_DoneThat yes its micro-siemens: https://en.wikipedia.org/wiki/Siemens_(unit)
I am using this unit: https://www.amazon.com/gp/product/B000VVVEUI/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
@BeenThere_DoneThat I’m using a 5-gallon bucket.
Ive been monitoring my temperature with no noticeable increase in temperature. Im engraving at 7ma for about 2.5min then a minute or so of reloading the machine.
Finally had a moment to run some new test cuts using the distilled/bleach approach, and while I was running with the ventilation fan on, I couldn’t really tell a difference in sound. I’ll turn off the fans and record a fresh video for comparison’s sake.
@Bob_Buechler so are you saying you still have the squeaking noise of above?
I believe so, yes. I’ll kill my fan temporarily, re-record and post it for review.
@donkjr There’s a procedure here to measure water conductivity. Could you try it and see if it gives similar results to your meter ?
@artag I have tried it. DC measurement does not result in an accurate measurement because of polarization effects, probe materials etc.
A DC approach may still be useful with some experimentation but since a conductivity meter is so inexpensive I moved on to other pressing investigations. I also wanted measurements that would accurately correlate to published materials.
http://www.analytical-chemistry.uoc.gr/files/items/6/618/agwgimometria_2.pdf