What order should I put the aquarium filter media?
There are many ways to layer the filter media in your filter, so these are our general suggestions. The first step is to look in the manual and find out which direction the water flows through the filter. As the water enters the filter media basket, we like to use a coarse sponge pad as mechanical filtration to block the largest chunks of debris and prevent them from entering the rest of the filter media. If you need to use the ammonia or phosphate media pads, you can place them here since the pads also serve as mechanical filtration. As a final mechanical filtration layer, you have the option of adding the fine poly pad to catch even smaller particles floating in the water.
The next layer is the biological filtration, so fill the media trays with bio media. Finally, you can choose to use chemical filtration like activated carbon or Purigen at the very end right before the water leaves the filter and reenters the aquarium. Not all of these products are necessary, but we do recommend having at least one layer of coarse mechanical filtration and then one layer of biological filtration if you have room.
For more information on filter media, read the full article here.