EDTA or ethylenediaminetetraacetic acid is a chelating ingredient we can add to our products at as low as 0.2% EDTA binds with metal ions (mostly calcium and iron ions) and keeps them from being reactive with our various ingredients. These metal ions can precipitate in our creations, forming a metallic solid that is really unpleasant. And the metal ions can keep our surfactant mixes from foaming as well as they should, and can remove the scum that builds up on the tub after a bath.
It is suggested you use tetrasodium EDTA for alkaline products (pH over 8) as it has an alkaline pH in water of 10 to 11, and disodium EDTA for products in the pH range of 3.0 to 9.0 as it has a pH of 4 to 6. We can use it in lotions and surfactant based creations at up to 0.20%, which is enough to do the job (but check your suppliers’ recommendations). Add it to your water phase.
To learn more about either of these, please click this link to find a longer post.