What Is Best Media For Fluval 306

Did you get the manual for the filter? Just in case you didn't, here it is http://ca-en.hagen.com/File/b3378f42-51ae-42e9-8c10-44fdc858d921

You will see that they suggest Biofoam in the lowest basket, biomax in the middle basket and a polishing pad and carbon in the top basket. There are also vertical sponges in what they call the foam screen frame.

The water passes through the sponges in the foam screen frame, which catch debris. Then the water travels upwards through the baskets. I would keep the sponge in the bottom basket as not only does that catch any debris that gets through the foam screen, it also houses the filter bacteria. Biomax is also a good home for bacteria so I would use that in the middle basket.
But you do not need to use carbon in the top basket on a routing basis, I would just use more biomax. The polishing pad catches fine particles that go through a sponge, but pre-shaped Fluval pads will be expensive. I would buy a length of filter wool (aka filter floss) and cut that to the right shape - much cheaper.