Disodium EDTA Acidity and pH

Regarding the acidity of Disodium EDTA, it has a slightly acidic pH (4-5) but is used at a very low concentration (typically 0.1-0.2%). This low usage rate means it is unlikely to significantly lower the overall pH of your product to the extent that it would degrade acid-sensitive ingredients. You generally do not need to add Triethanolamine (TEA) specifically to counteract the slight acidity of Disodium EDTA.

Preservatives in Vitamin C Serum

For a Vitamin C serum like the Skinceuticals C E Ferulic type, even though the high acidity makes it difficult for bacteria to grow, it is still highly recommended to include a preservative if you do not plan to store it in the refrigerator. While refrigeration helps slow down the oxidation of Vitamin C, a preservative is necessary to prevent microbial contamination and ensure the product remains safe for use throughout its shelf life, especially if stored at room temperature.