The first picture looks like the coarse or larger ceramic media. The main function of this media, besides being a platform for the beneficial bacteria, is to slow the water flow, causing it to go in many directions as it hits the cylindars. When it slows and swirls around in the filter tank, the larger debris will fall out of suspention and remain in the bottom of your filter. This would go in the bottom layer of your cannister.
Typically you would also include a layer of course filter type floss or spongey stuff to would also filter out the large debris.
On top of that goes the layers of whatever you wish to use for your biological filtration.
Lava rock can work as an excellent platform for bacteria. It tends to have "dust" and be difficult to get "clean". It is sharp and right after it breaks you will get loads of cloudly lava dust in the water. You will need to wash it extremely well. If left in larger chunks (3/4 inch or so), it would break up the flow of the water a sort out large debris. It is not as fine a pore as the bioballs, so it would do well going before the biobalos.
The Bio balls, being an especially fine quality of media would best be put on the very top of your stack. Fine holes in them can get plugged up with large mulm and debris, so having them after the majority of the large debris has been removed is ideal.
Between or at least on top of all, you would want a fine polishing filter floss or pad to polish the fine debris from the water.
So I would suggest #1 on the bottom, a coarse filter pad, #3 lava rock in the middle, maybe another finer filter pad if you wish, and then #2 the bio balls in the top layer with a fine filter pad for polishing on top of all.
Does that help?
