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Re: kitty litter substrate

On Fri, 16 Jun 2000, David A. Youngker wrote (quoting me):

> > Some clay products - including some types of kitty litter -
> > contain plant-available calcium and magnesium carried
> > over from its previous environment.  Other clays -- notably
> > the sodium bentonites that may be used for clumping kitty
> > litter -- may contain no nutrients at all.
> What nutritional value does laterite hold? Or is its appeal in the iron
> content alone?

None I know of other than the iron, and no-one but Tom Barr responded on
or off the list to tell me that they were able to run a tank with laterite
as the sole source of iron, so I don't know how good it is as the sole
iron source. And I think Tom could probably grow plants in a bed of broken
glass.  But what does that have to do with kitty litter?
quoting Dan Q.:

> "Kitty Litter allows the plants to grow healthier roots, but also root
> hairs, that they won't grow in sand or gravel."
> Why? Simple. I've tried everything from gravel to marine sand, and the one
> thing I personally have found to be true is that the finer the substrate,
> the more well-developed the root system. Including the "root hairs" that Dan
> mentions.

Many silty soils would provide the same advantage.
> So here comes Dan, talking of things I'd already known but hadn't "clicked
> on" because I was too entranced by what I was reading in the aquarium trade
> up until then. And he only points out the obvious - most aquatic plants do
> *not* grow in sand or gravel. Yet we beat our heads against the wall in a
> constant effort to get the best results from the most barren of substrates,
> constantly adding this and that just to get it *prepped*.
> Did'ja ever go wading for plants and *not* get stuck in the muck at some
> point or other?

Yes, I have.  I've seen large, burgeoning stands of Heteranthera dubia
growing out of submerged cobble banks cemented solid with calcium
carbonate.  I've seen a wide variety of aquatic plants from small
potamogetons to large water lilies growing in fairly clean, firm sand.
I've even seen Elodea growing out of cracks in bedrock.  Aquatic plants
aren't that picky about what they grow in.

Dave Huebert pointed out over and over that aquatic plants grow best in
silty soils.  Most places where I see lush stands of aquatic plants the
substrate is silt or fine sand, but often covered with a layer of stinking
organic muck supporting a whopping huge population of creepy-crawlies.  
Almost as often the substrate contains layers of calcium carbonate slime
originating from biogenic decalcification.  That doesn't mean that I want
any of those things in my aquarium.

And none of those natural substrates are pure clay.  Pure clay is a fairly
poor soil.

> Another point to consider - why would aquatic plants have developed the
> ability to transport water, air and nutrients down to a well-aerated,
> circulating substrate?

Aquatic substrates are often quite rich in organic matter.  Even a coarse
substrate with a substantial organic content and some water circulation
can be anaerobic.  Conversely, a fine-grained substrate without organic
matter in it (like a clean kitty litter substrate) may never get
anaerobic; anaerobic conditions are created by bacteria dining on organic
> > In order to allow circulation, the substrate needs to be built of a
> > small amount of kitty litter mixed with a larger amount of medium
> > to coarse sand or fine gravel.  Kitty litter probably should not
> > exceed 10% of the mix by volume. The sand or gravel allows water
> > to move through the substrate and the circulating water can reach
> > and replenish the clays.  With more than about 10% clay by volume
> > the circulation may be substantially blocked by the clay.
> Fortunately, this is not the case in practice.

I don't know how practice establishes this.  
> My substrate begins with around 1-1/2 inches of kitty litter, mixed only
> with Osmocote and Iron sulfate. (I used to use Tetra Initial Sticks, but
> dropped them in favor of the sulfate.) The low end of the tank has another
> 1-1/2 to 2 inches of straight, fine sand as a sealant/cover. Total depth at
> the high end can reach over 8 inches. My only concession to "turnover" is
> the introduction of Malaysian Trumpets.

The plants themselves can generate water turnover in the sand part of the
substrate by actively pumping water from their roots to their shoots. The
water they lift from their roots is replaced by water moving down through
the substrate to the roots.  This water can't circulate through clay
unless you have somehow left continuous openings through the clay layer.

> As to how well my plants fair - well, stay tuned for the CD that will be
> available with an entry into the AGA's International Aquascaping Showcase
> and Contest. That will be the first public introduction to my tanks after
> all these years. Once that's settled, I'll finally start illustrating my Web
> site.

I guess that answers the question about whether anyone has had success
using a solid layer of kitty litter in their substrate.  I'm not about to
disagree with your success.  Lots of people on this list can claim great
success with a variety of different substrates.  That's partly because
aquatic plants will quite happily grow in a lot of things, so success
alone doesn't differentiate between substrates.

My point is that if you want to use kitty litter there might be better
ways to do it.  I've used it mixed in small quantities with sand/gravel
both as an amendment for individual plants and as a full tank substrate
and I didn't have the problems that others responding on this thread

Roger Miller