Originally Posted by AVN
I don't see any reason why it would increase the lifespan of it.
Why not? Most of these substrates work by releasing things to lower the pH like humic acid, tannis, etc and absorb things like gh/kh to help keep it stable, so why do you think say 20L of soil wouldn't last longer than 5L of soil? 20L would be able to release things for longer and absorb longer.