You may want to look at the Bubble-Magus line of skimmers.
www.nuocean.com sells them out of Brooklyn. I have their nano skimmer and it does a great job. Here's a link to the biggest external that nuocean sells:
http://www.nuocean.com/skimmers/bubb...0-skimmer.html
I think it's always best to assume they over-estimate skimmer abilities so it would probably be the right size.
The customer service from these guys is good, my collection cup was cracked in shipping and they took care of me immediately.