Wrong again furballi.
It's not the pH drop that kills the fish. It's the high levels of CO2. The pH drops because because of the CO2.
And kH has nothing to do with it. It takes 30 ppm of CO2 to drop the pH of the water 1° no matter what the kH. That assumes of course that you are starting with a tank with no CO2 injection. But that first degree of drop takes ~30 ppm of CO2.
What part of "Low pH is the symptom and not the problem." did you not understand?
I will say it again and type it slowly so you can understand. pH changes caused by CO2 have no effect on fish. Of course if you get so much CO2 into the water that their gills can no longer function then you will harm the fish. But it's NOT the pH that causes that problem.
I have covered the reasons why pH changes due to CO2 do not harm fish in my FAQ. www.theplantedtankfaq.com
Also Tom Barr has shown that pH changes due to CO2 do no harm to fish.
Using CO2 to lower pH is an artificial means to do so. It does not change the hardness or TDS of the water. Normally when you lower pH you are also required to change the hardness and TDS. If this change occurs quickly you can cause problems with the osmotic balance of the fish. When CO2 is used to lower pH there is no change in the hardness or pH.
Again.... and I know it's hard, but you have to separate the pH and the CO2 levels. High CO2 levels will cause low pH. But the low pH is the symptom, not the problem.