Can anyone suggest an in sump skimmer for me?

[Slick Fork]

I'm going to agree with those saying keep what you've got until you can afford a reasonable upgrade. Trading a decent skimmer like yours for a bargain brand which claims a higher capacity but doesn't work as well isn't a really good option.

Do a search over at reef central for the vertex skimmer club, I skimmed a few posts over there discussing replacing the pump and the MASSIVE difference it made in skimmate production. That might work out to be the most cost effective stop-gap measure for you. I can't recall if the In-80's were discussed or not.

Where does the 20" height restriction come from? Your stand? I can't imagine any skimmers rated for that size of a tank that would fit in there. I have an In-180 and I need at least 25" clearance. If it's the way the sump is designed you may have to bite the bullet and buy a new sump to fit a properly sized skimmer.