What if the DI isn't filling all the way up?

New DI filters take time to get saturated. I've personally observed it taking as long as two weeks until the DI section stays full. Don't worry, because the water can only get out one way - through the media and it will be de-ionized.

If the DI media cartridge is installed upside down, that needs to be corrected immediately. The side of the cartridge has an arrow which should be pointing straight up, and the black flat washer should be at the top when installing it.