wow! your gettin' pretty tech there, i like it!
just so you know..........pretty much any power filter on the market provides all three levels of filtration. the floss is, of course, mechanical...............the carbon and/or ammo chips are the chemical filtration...........then the walls of your filter, the gravel, the filter floss and even carbon/ammo chips house all the biological filtration. going through all the costs of micron bags and whatnot will just be "extras" that would work better as a once/twice a week water polisher. i would suggest just getting filter floss sheets and cut them to your filter cartridge plastic. you stick the floss to the plastic with either paperclip, silicone or something nontoxic.
if you are thinking of "making" a diatom filter out of a power filter, it just wont work. you have to force the water through the bag w/diatamecious earth (from the inside out). besides that, it isnt recommended to run a diatom filter on any tank continuosly. it should be used as more of a "water polisher" once or twice a week (or when needed). maybe you should check out my diy micron filter thread in the diy forum. it really works well!
tooth