Needs a pretty good light. WPG is not a good rule, and I don't like to use it. CO2 isn't necessary, but will help this plant to carpet your foreground. It will not climb the glass.
Everything I've read and been told says that that isn't enough light to get HC to grow as a ground cover. You'd need a really shallow tank for it to carpet your substrate with that amount of light. This is just what I've read and been told though so I cannot pretend to be an expert on it. PC lighting just doesn't penetrate the water well enough.