First the water flow in it. Goes down inlet tube then up the white foam pads , then to center baskets down to pump and up outlet tube.
Oh , the flat black pad is impregnated with carbon ( which will buy you a few weeks before you need to get some ) and the one with bumps for more surface area is for bio use. Myself I add carbon , also purigen ! Buy bulk much cheaper than those premade ones.
That being said this is what I do personally for my 125 gallons water. I first remove the red part in baskets , I want every cm for more media.
TOP basket : I place a media bag with 1 to 1 1/2 cups carbon and another media bag with 3 - 6 oz's of purigen , yes more purigen than I need but I want crystal clear water . Normally only need about 2 oz's per 100 gallons. Directly on top I use the flat black pad to protect my media. the middle and bottom baskets are filled with only bio rings no pads. NOTE do not try to over fill top basket that's where it purges the air out ! Read page 10 step #4 carefully. It works well for me , look at some of my videos on forum to see.
In time you can but some blue pads (fine) works well too. Or even a white pad (polishing pad ) but they clogged up very fast needing more cleaning. And you know how we all just love doing extra maintenance !
Also you can play around with the outlet nozzle for different type of flows. Myself I don't use the nozzle just the open pipe but I need to see better from a top view using a stock tank.
Good reading here :
viewtopic.php?f=9&t=30145The carbon is for any toxic chemicals in water like chloramines.
Purigen is for organic matter.
Some say cost to much (purigen) but it can be regenerated several times making it very cheap. Unlike carbon that "must" be changed once a month ( get saturated with toxins) the purigen last about 6 months depending on bio load before it needs changing ( will turn black when change is needed). Regenerate it and have ready for next 6 months to change it.