dudley has it right. I have seen people use lava rock, like for grills or landscaping, broken into smaller pieces but not the sand...
If you just want more mechanical media in your filters you could use thinnish foam or stiff floss-like polyester (less dense than floss). Bacteria will colonize those too. Both are available in sheets that you cut to fit (I think). I have a poly sheet someone gave me but no packaging to help.
Do you really need more media?
If you just want more mechanical media in your filters you could use thinnish foam or stiff floss-like polyester (less dense than floss). Bacteria will colonize those too. Both are available in sheets that you cut to fit (I think). I have a poly sheet someone gave me but no packaging to help.
Do you really need more media?