In the paragraph in my article that start "How should I add it to my soap?", I recommend adding EDTA to the fats, and then adding the lye solution. I intended the next paragraph to be an explanation of why I recommend what I recommend, but obviously I missed the mark. I will delete the explanation paragraph entirely.
As far as how to use a 50% EDTA solution, that's in the article too. Here's an edited version --
"...You can make an EDTA solution in any concentration up to about 50% by weight (50 grams EDTA and 50 grams of distilled water). Measure the desired amount of EDTA powder and mix with distilled water until the EDTA is fully dissolved. Store in a labeled, airtight container.
"...here is how to calculate the amount of 50% EDTA solution to use...:
"50% EDTA solution weight = 2 X EDTA powder wt
"...If using an EDTA solution, blend it into your fats along with any other additives you want to add to the fats, add the lye solution, and soap as usual. If using EDTA powder, mix the powder into the water or water-based liquid in your recipe until the powder is dissolved and blend this mixture into your fats...."