While I have seen reference to bio-balls on one beckett design ... the majority of them are " bio-ball free "
the recirculating beckett is a interesting idea however ... I have seen this mostly in the pinwheel designs.
As far as pumps go you will definately want 2 mak 4's to run a dual beckett ( especially if one is for the sump and the other for recirculating )
a mak 5 would be best but who has the $$ to run one on each beckett ?
so you have been building this thing since March ? ... gonna finish it before Xmas ?
PS ... here is the skimmer design for my next DIY project
http://reefcentral.com/forums/showth...&pagenumber=53
http://www.weatherson.com/index.htm
he uses a iwaki md100rlt ( 2150/hr ) ... which is a little less than running 2 mak4's ... no bio-balls though hehehe