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Re: Sand in substrate

"Mortimer Snerd" <mortimersnerd at uswest_net> wrote:

> All,
> At the risk of restarting the substrate wars, or even igniting a minor
> skirmish, I'm going to ask my question.  I recently had a conversation with
> Karl Scholler (of Substrate Gold fame) about my 100 gallon I'm rebuilding
> after my recent move.  He suggested I use an inch or two of sand mixed with
> laterite under 2-4 inches of gravel, stating that he found it was the best
> way to work with most plants, especially those that were heavy root feeders,
> like crypts and swords.  I'm interested in trying it out, but have concerns
> about the sand compacting, putrification and the plants becoming root-bound.
> As a bonus, I use Dupla's heating cables, and am wondering if there is a
> possibility the sand will reduce the theoretical circulation of water
> through the substrate via convection.  Any thoughts much appreciated.
> Justin Collins

I have a 1.5 year old planted aquarium in which I used sand mixed with
Substrate Gold and smashed vermiculite, topped with pure sand, topped in turn
with gravel. The sand is silica sand used in pool filters. The results so far 
are mixed, to the point I would rethink the use of a deep sand layer in  
future setups. 

I agree with Karl in that sand topped with gravel is better than pure gravel 
to hold plants in place, and the roots seem to love the finer medium. It also 
does a great job in sealing the laterite powder from clouding the water, even 
when uprooting, and keeps the Jobe's spikes well sealed out as well. On the 
other hand, after all this time, it compacted to an extent that the initially 
4" deep layer at the back of the tank compressed down to 3.5" now. I recently
did a major uprooting/poking/mixing of the entire substrate (except the crypt 
lawn) to avoid a root-bound condition (as per Karen Randal's suggestions), 
and found a couple of places where anaerobic conditions developed. These 
where at the very surface of the substrate, apparently because the place was 
sealed from the water column by either a flat stone or a flat piece of 
drifwood. I found nothing similar at the places where rooted plants thrive, so 
I believe the condition was not directly related to the substrate interior 
structure and compaction. 

Anyway, based on that experience, I would try to avoid a pure sand substrate.
I would try instead a partial mix with a coarser grained gravel or similar
material, or avoid the sand entirely. It seems to me that water circulation
and/or solute diffusion thru interstitial spaces in the substrate is a
important mechanism that we should try to keep working. On the same grounds,
my feeling is that heating cables would be of no use in a substrate made of
any compact material. Btw, this tank has a slow flow UGF plate in place, and
that doesn't seem to make a dent in the tendency of this substrate to 
compact. Will get rid of the plate when I redo the tank.

Good luck !

- Ivo Busko
  Baltimore, MD