Just to clarify, any lye will lose purity over time every time you open the bottle and moisture from the air gets in. The drain cleaner that says 100% lye, in my mind, is saying it started out with no extra additives from the standpoint of production. Knowing a bit about the chemical reactions of lye, means I take every precaution to keep the seal on the lye container air-tight between uses, and never leave the lid off for longer than necessary and that I avoid introducing moisture into the container.