My suggestion would be not to do the test. I have done that and it is not going to be good. When you do take vitamins or electrolytes you feel great at that point but the harm comes later. Also the harm is not measurable. In my case I started bloating a lot after my fast and felt sick. I used salt even though I have never felt terrible weakness or detox symptoms as our fellow fasters go through. I also brushed my teeth with salt.
I did not have ketone strips 12 years ago when I did this, but that would be a good way to measure that body is in ketosis or not when supplementing during water fast.
Remember digestion begins in our mouth. Most carnivores don't have that, they gouch out meat and swallow it. We chew everything, so even putting water with some supplement starts the digestion. Why would you do that when abstain from food?