Siporax

[davej]

Just a note to clarify.
anaerobic by definition :

Occurring in the absence of oxygen or not requiring oxygen to live. Anaerobic bacteria produce energy from food molecules without the presence of oxygen.

[Potatohead]

I stand corrected... I think the same principle applies however

[emerald crab]

I use "Hydroton", it works fine for me. I've been using it for 5-6 years and I'm happy with it.