The sponge should be first in the direction of waterflow to stop the ceramic/plastic media getting clogged with debris. The filter wool should be last in the direction of water flow to remove the tiny particles that went through the other media before the water goes back into the tank.
The APS manual says the water flows up through the media so the sponge should be at the bottom and filter wool at the top.
The APS manual says the water flows up through the media so the sponge should be at the bottom and filter wool at the top.