vermiculite substrate

>I'm planning on tearing down my tank soon and want to use a better substrate
>for my plants (as opposed to just gravel).  I found laterite but it's kinda
>expensive.  After reading through most of the net posts on laterite, it
>seems the primary advantages of laterite are as a chelating region and its
>ability to remove phosphates from the water column.  If vermiculite has a
>higher CEC than laterite, it would serve adequately as a chelating source.
>I wanted to mix 1 lb of laterite with 2 lbs of vermiculite (well wetted) in
>the bottom third of my gravel, thereby obtaining a substrate with a high
>CEC, phosphate removal capability, and lower cost. I have 160 watts of light
>over a 100 gallon, no substrate heating, and DIY CO2.  Will this work?

Vermiculite is a very light (like popcorn) substance.  I'd estimate that 1/8 lb 
of vermiculite takes up as much volume as 1 lb of laterite when dry.  It does 
compact some when wet though to about twice its dry density.  I purchased 1 lb 
(roughly 1/4 ft^3) of vermiculite and used half of it by itself to cover the 
bottom 1.5" of my 20g, covered by blasting sand.  A nice thing about 
vermiculite is that if it gets in your water column, it settles right back out.

It's too early to tell how well it works, and my 20g is currently completely 
stuffed with plants (stacked on top of each other) until I get my 55 set up 
again.  I installed an under gravel manifold for fertilization and to help 
reduce anaerobic tendencies, but have so far only used it for fertilization.

Hope this helps,

David W. Webb
Enterprise Computing Provisioning
Texas Instruments Inc. Dallas, TX USA
(214) 575-3443 (voice)  MSGID:       DAWB
(214) 575-4853 (fax)    Internet:    dwebb at ti_com
(214) 581-2380 (pager)  Text Pager:  pgr at ti_com Subj:PAGE:David Webb