Replied by Ted (Bangkok, Thailand)
Potassium Chloride is NOT going to work because its pH is only 7. You need an alkaline form. Try Baking soda as a substitute instead, it is a weaker version but works too.
How does one make it into a 20 or 15 percent solution
For baking soda, in you can just add as much baking soda until it can no longer dissolve itself in the solution. This is easier for you without the math. Again, I would much prefer a stronger alkaline solution but this will do.