well, i got the idea from aquaultraviolet.com re: ultima II
http://www.aquaultraviolet.com/filtration.html
they (AquaUltra) claim that the ultima II units need only a vortex before it for it to act as a biofilter. if you check their sizing, you'll see that they have this UII 20000 rated for 20000 gallons, (they explicitly claim that this is not an overexaggeration of capacity) of course i dont believe them and i proceeded to add to my layout two units of the same size and then another the same size as the UII 10000 - thats 30000 "capacity" on a 14000 gallon pond. im thinking of putting japmats in the vortex themselves as "backup" i can aerate these too. but i figure i can put no more than 10 jap mats in the vortex units 1meter diameter by 1meter-4feet deep.
this is a pretty big pdf file but on page 8 of 22 (page 5 actually) is where they claim that their filter capacity are not exaggerated.
http://www.aquaultraviolet.com/instr...aIIInstall.pdf