I use dyna-roc in all my mixes. It is a pourous rock, it absorbs 150% of its own weight in water and doesn't decay. 2 months ago I seperated a phal into two pieces and planted one in my regular mix(fir bark, coconut husk chips, and fine dyna-roc), the other in straight fine dyna-roc. I have treated each the same as far as watering and fertilysing and they both seem to be thriving. If you are intrested in dyna-rock you can find it on line at
www.dyna-gro.com