i have that same skimmer. mine is used as an HOB though. that foam pad in the collection cup is absolutely useless. since i took it out and replaced it with a small amount of filter floss i have zero micro bubbles. since yours is in the sump you might try getting rid of that box altogether.

there were many growing pains with that skimmer and it took about 5-6 months for me to get everything figured out and set the way i wanted it, but its a great skimmer for the money.