EDTA, Ethylenediaminetetraacetic acid is a molecule which complexes metal ions in aqueous environments. It is available in four neutralizations, two of which, Disodium EDTA and Tetrasodium EDTA, are commonly used in the cosmetics. Generally, the choice of which product to use is determined by the pH of your product, but this is not a hard and fast rule. Disodium EDTA is commonly used in neutral to mildly acidic products, like most creams, lotions, and neutral pH liquid soaps and shampoos. EDTA works synergistically with your preservative to improve preservative efficacy.
Disodium EDTA has limited solubility in water, but at a typical usage rate of 0.2% to improve preservative efficacy, even if not fully solubilized, it is still efficacious. In creams or lotions, there will be no grittiness and it will not be seen. In clear or transparent gel, serum, or clear surfactant systems, use Tetrasodium EDTA, which is highly soluble in water. At low usage rates, it will not raise the pH unduly, but if it does, you can simply lower the pH of your formulation with a citric acid solution.