Review of AHA 20% Formula

Regarding the formula you provided (Water 68.5g, AHA (Glycolic Acid 70%) 29.0g, Pro Polymer 1.5g, Disodium EDTA 1.0g, totaling 100g), the proportions are correct for achieving an approximate 20% concentration of pure AHA (since 29g of 70% Glycolic Acid contains approximately 20.3g of pure Glycolic Acid).

The use of Disodium EDTA in this formula is appropriate because you are not using cosmetic-grade distilled water. Disodium EDTA acts as a chelating agent to bind ions in the water you use, preventing them from interfering with other ingredients in the formula and helping to improve formula stability.

Regarding your question about adding a pH adjusting ingredient directly into the formula, this is not possible. As the staff mentioned in the conversation, AHA needs to work in a highly acidic environment (low pH) to be most effective. If you mix a basic substance into the formula from the beginning, the AHA will be neutralized and lose its efficacy before you apply it.

Therefore, the correct method is to adjust the pH of the skin after using the AHA product. You can use Sodium Bicarbonate mixed with water as recommended by the staff, apply it to the face, and leave it for about 15 minutes to help return the skin's pH level to normal.