I would fill one basket with a quality ceramic or sintered glass bio media. The other two baskets are optional. Taylor to your needs add more bio media or chemical media or micro filtration pads(though many have found these can clog quickly)
More info such as tank size and intended amount/size of stock along with a general description of the decor in your tank will also be helpful.
Alright so its a 180 gal, its currently on order, but i would like to get the FX5 up and running ASAP on my current tank so that it will be cycled already. the 180 i would like to have 12 discus (i have 8 current but i would like some more), 2 scobina rays (courtesy of Scobinaman ) and either some clown loaches or some cardinal tetras. a couple L260s will be on c/u and thats what i was thinking. is that over stocked? i know your supposed to have 1 discus per 10 gallons but seriously thats kinda of a "beginner" rule lol. as for Tank decor i was thinking a bed of the whitest quartz based sand i can find with two rock "islands". one in the right hand corner and the other somewhere mid to left hand side. they wont be too big because i want the rays to be able to swim around them. i will have drift wood coming off the "islands" in a sort of ravaged by hurricane and then burried way. i will have some plants but i was thinking of potting them and putting the pots under the rocks as well as attach some java ferns and other similar plants to the driftwood above. thats the plan at least lol