I found this post in Google. Just for your information, I don't feel that the 9415 is so excessive... looking to the Tunze USA data:
http://tunzeusa.com/new-9415-doc-protein-skimmer/
400 gallons for a Fish Only system
320 gallons for a Soft Coral system
240 gallons for a Mixed Reef
160 gallons for a Stony Coral dominant system