I would suggest the Aquatrance 2000s http://www.coralvue.com/aquatrance-2000s-skimmer-pump
It will require a new plumbing kit but will provide greater performance than the OTP 2000. We do plan to have a smaller RO-DC pump and I believe it will be capable of running externally. More info on these new DC pumps will be available after Reef Octopus returns from Interzoo.