Re: sand, clay, soil...substrates

Wright Huntley wrote:
> Date: Sun, 28 Jan 1996 07:36:20 -0800
> Subject: cc: from rec.aquaria
> Jerry A Morelli wrote:
> >
> >My girlfriend would like to use sand as a substrate in her 55 gallon tank 
> >that she plans on using for cichlids.  Is this OK?  Also, how would you 
> >go about cleaning the sand?
> Vacuuming works OK if you use a larger-mouth vacuum tube and smaller hose to 
> avoid sucking the sand out. A layer of coarser gravel over the sand works, 
> too, but you need to resist the urge to plunge the vacuum too deep.

Old habits die hard. ;-) In the days of under gravel filters and no plants
we relied upon a healthy colony of nitrogen consuming bacteria to 
eat the toxic levels of ammonia generated by our (typically) over
populated tanks. The bacteria relied upon a good circulation of oxygenated
water through the substrate or it would die off. So we invented gravel
washing, the neat little plastic tube you shove in the gravel and siphon
off clouds of yucky fish doo-doos. Without regular gravel washings, the
substrate became so compacted that the bacteria wouldn't get enough
oxygen and the water didn't circulate enough and the ammonia concentration
made the fish sick.

Let's assume that Jerry's girlfriend has lots of aquatic plants. If so
then sand would probably be ok. If she's relying upon a UGF to consume
ammonia, then no, it's a bad idea. Too little circulation.

With a planted aquarium, we no longer have to be concerned about the
toxic ammonia because as long as we have enough plants, light, CO2 and
a few other essentials and not too many fish, the plants very happily
consume all the ammonia/ammonium that our fish are able to generate.
In fact the solid fish wastes make excellent compost for the plants.

Now we discover that one of the critical elements we need in our aquatic
systems is iron; not just any iron, but the soluble Fe-(2) which is
produced by a different kind of bacteria in an oxygen depleted environment
at the bottom of the substrate (where there is no UGF plate!). In fact,
if we have iron rich clay, or soil (soil contains iron), there is a 
steady supply of iron which our plant rootlets and root hairs can
absorb. Ideally, there should be a layer of dense, fine clay with a
high iron content and a source of heat at the very bottom of the
substrate. Over this layer, another layer of soil (perhaps mixed 
with vermiculite, peat or gravel) and probably several solid fertilizer
tablets or plant food sticks available from the gardening section in
your local department store. On the surface a layer of gravel 
or sand (to make planting easy and keep from getting clouds of fine 
sediment stirred up). This is just a refinement of the very, very
budget minded substrate described by Jim Kelly in a recent issue of
TAG (the AGA periodical). I'm suggesting a three layer approach instead
of two and heating to promote biological activity in the substrate
(not circulation as suggested by "The Optimum Aquarium" method).
I'm also borrowing ideas from Paul Krombholz. The bottom layer is to
promote the anaerobic conditions needed for Fe reduction. Vermiculite 
would be used to keep the middle layer soil from becoming compacted 
and to maximize root penetration.

Back to the original topic:

We no longer need to "wash the gravel". I still prefer to very lightly
suck up any floating debris when I'm doing water changes on the theory
that this rotting material might use up too much oxygen and provide
a home for some kinds of unwanted bacteria. I'm concerned about stirring
up the substrate too much because that sediment contains a lot of
nutrients loosely attached to the CEC binding sites or just dissolved
in the water within the substrate. I even put solid fertilizer tablets
down in my substrate now and I sure don't want to disturb the substrate
around them. That could be a sure fire recipe for a green water algae
bloom especially in a high lighting tank.

Since I got into plants, I have never had an aquarium go through the
"Nitrogen Cycle". Start off with fast growing plants, CO2 and iron
and not too many fish to begin in your next tank and prove it to yourself
by measuring the ammonia everyday. Better yet, put a layer of soil in 
the bottom of the tank and give up your old UGF. Happy gardening!

Steve (in freezing cold Vancouver but still great skiing :-)