Oh hey 2easy, I thought I might mention Scoria (aka lava rock) to you for possible use with aquaponics.
I recently bought some from bunnings (pieces roughly the size of standard clay balls) to replace perlite in my soil mix.
Anyhow it doesn't hold as much oxygen in it's pores as clay balls but it has trace elements in it which may be able to slowly release into your system. I was thinking maybe you could either use the lava rock in place of clayballs entirely or maybe just go half-half or what ever.
Food for thought maybe?