I just flushed out my water heater and replaced both elements and had to pull one to add teflon type and noticed the build up was already starting not even a half hour later why would this be

I just flushed out my water heater and replaced both elements and had to pull one to add teflon type and noticed the the build up was already starting not even a half hour later why would this be

Are you on a pump or city water? My bet's on the pump. Cheers, Tom