Sponge rock? Not sure what that is, where do you get it?

My experience with CHCs and coir thus far have been that I don't see any useful role for the perlite to play. The coconut media is already very light and porous. A little too light in fact if you have a tall tree. I have to stake my Key lime pots in the warm season because the media in the pot doesn't weigh enough to keep the pot from blowing over in the wind.

.....Alan.

I have never used a CHC/perlite blend, so I can only make assumptions. My guess is that the combination could work OK. However, two items of concern to me would be, (1). a 50/50 CHC perlite blend would constantly create a huge mess, and (2) I think the perlite would begin separating and would rise (float) to the upper portion of the container with each irrigation. - Millet

This may be a dumb question, but does Perlite have any water holding capabilities? If not, I would think this would be another reason to go with the CHC.

Phillip

I'm sure perlite has water holding capacity-- I don't know how it compares to CHC, but you can measure it by weighing some before and after wetting.

http://www.hort.cornell.edu/department/faculty/good/growon/media/inorg.html
Perlite has a very low cation exchange capacity, low water-holding capacity (19%), and neutral pH. The closed-cell composition of perlite contributes to its compaction resistance, enhances media drainage, and heightens the aeration porosity of peat-based media (Bilderback 1982). Because perlite contains only minute amounts of plant nutrients, liquid feeding is a practical mode of fertilization. Be aware of possible aluminum toxicity in acidic media (pH < 5).

.....Alan.

Interesting discusion.I read somewhere the other day of them growing citrus in Isreal in pure perlite in huge see through containers outside shopping malls! Denser grade towards the bottom and fine in the growing zone,with stones/bark on top.They where impressive,in clear plastic containers.I would imagine it gets pretty hot there,so they must hold some moisture.I thought citrus didnt need much moisture anyway.I also read citrus can survive on low levels of water.
I have been using 50/50 potting soil and perlite and its been great.There is a lot of rain here and our temps dont go over 25c. I read that if citrus roots remain saturated for more than 48hrs then damage starts to occur.Well,this mix dries out nicely and im not killing anymore trees from lack of oxygen to the roots.I also read that insects hate perlite as well,so thats a bonus.
However,after millets experiment i might well give the coir/chc
a go.Could i use gypsum instead of dolomite lime?we dont have stem over in new zealand either.Cheers

I find perlite to be problematic if used in quantity. Over time it tends to percolate to the top after repeated watering of the medium because of its light weight combined with its air holding capacity. Would larger size perlite be any better (or worse)?

I havent noticed coming to the top of my mixes but i do water gently with a watering can.Not all at once,just little bursts and let it drain.Once you have watered the top,it tends to compact a bit and then repeat until draining.4 or 5 waters in one go.Hope that helps.

Junglekeeper I was thinking of about 10 -20 % perlite. Laidbackdood have you tried watering from the bottom. Put the pot in bucket of water and after it soaks the medium remove it from the watering bucket and fill the top of your plant pot with water to flush any undesireable buildup out. Bottom watering only works if you are not trying to pickup a 15 -25 gallon pot.