Re: cables from the UK

[Thomas Barr <tcbiii at earthlink_net>]

First off Dupla Cables have very good suction cups and stay in place better
than any cables I've ever seen or used.
These cables need to be in place in order for them to work correctly if you
want to proscribe the arguments below. Simply laying some wire etc on the
bottom of a tank doesn't fulfill this requirement.

Copied from George (where is he anyway?:-):

> 1) Provide warmth in the substrate for certain plant species (Barclaya
> longifolia, specifically).  In this case the substrate should be warmer
> than the water.

Why? In nature the substrate is often the coolest part. If the substrate is
white sand, it will certainly be cooler. If it's black stagnant mud in
shallow clear water, then it will be warm but only the top cm or two
generally. Also depends on wind and upper mix layer circulation. I could go
on and on here. Natural systems are not like coils down 10 cm deep as the
heating source. The source of heat in natural systems is the sun. Water
color and turbitity also play large roles.

The notion that this is something based off nature that can be generalized
and a natural processes is a big stretch. Nature has many different
environments that aquatic plants live and thrive it.

This is one of the reasons why I am putting together a field trip here in
FL, to show folks the wide variety of habitat.

> 2) Provide warmth in the substrate to speed up biochemical
> processes.

Well, here's the main thing. But this assumes that you need sped up
biochemical processes at all. If there's less in/out, then the roots should
have difficulty getting what they need and creating the reductive
environment that they need but we don't see this(Like most folks that do not
have cables).

Roots don't just sit there, they are not passive.

They are active and pump O2 and H+ down into the root zone.

Adding heat another 1 cm deeper on the outside of glass will not change
anything significant for anyone to ever worry about.
I stand by the reptile pads if someone wants to try it out for themselves
and it will not cost much/nor cause you to uproot a tank, it's easy to add.

> 3) Transport nutrients from the water into the substrate.

Use root tabs/laterite etc if you feel this is needed.

> Important
> nutrients would be ammonium (fish waste, etc),

NH4 should be removed quickly by the leaves, not the roots.
Some build up,and breakdown of organic matter eventually works it's way down
into the substrate but the flows in/out of the substrate are TOO fast to
maintain a better reductive environment than no flow at all.
Diffusion alone is enough to have an optimum flow rate in/out of a
substrate. Tropica agrees and their case study tank showed that cables
provided too much flow. I've used cables for years, I've used 500$ systems
and made my own as well. I am not the voice of inexperience on this issue.
Substrate was an obsession for sometime.

> iron (from trace
> element additions),

Well why add iron to the substrate then?

> calcium, potassium and other trace elements.

Adding Ca and K won't help. These are provided by the water column and can
be taken in by the leaves. The other traces are very debatable.
 
> This 
> will replenish nutrients used by the roots and provide long
> term viability (in terms of years).

My tanks and plants are quite viable, I don't use cable or pads these days.

4) Transport harmful products out of
> the substrate.  Decomposition products may be harmful to plant roots.

There's plenty of flow to remove anything w/o cables.
  
> There is also conjecture
> that plants give of low level toxins to keep other plants out of their
> territory (successful weeds have made this an art form).

Show me one submerged aquatic that does this. Aquatic plants have little
reason/advantage in doing so. The chemicals will be washed away and the
plant has no way of "knowing" how large a water body they live in nor if
it's flowing etc. The environment aquatic plants live in variable.
Allelopathy is often talked about but truthfully has very little influence
in algal control or plant-plant interactions in aquarium plants in the
studies done to date.

> If these toxins 
> build up due to poor circulation, the plant may
> harm itself.

I don't buy this idea one bit. Diffusion is plenty fast enough to bring this
out of the substrate. Water changes provide plenty of export for any
"toxins". And what about non Carbon enriched tanks? I don't change the water
for months on end, the most plants don't harm themselves there.

> 5) Provide a chelating medium that binds the divalent state
> of trace
> elements with an organic molecule, enabling the trace element to be
> adsorbed by root hairs.

We can and do use a number of chelators. Plants can also use rust and reduce
the iron to take it in. Folks can use iron filings, rust etc to add iron the
gravel if they want. I've done it.
You can add peat also. Chelates, reduces etc and provides a good source of
organic matter till the tank matures well on its own.

> 6) Provide a reducing rather than oxidizing
> environment so that trace elements are kept in their divalent state (usable
> by plants) or
> are reduced from their oxidized trivalent state.  Iron especially will
> rapidly oxidize in water with normal levels of oxygen.

So lowering the flow rate would help, cables provide too much flow rate.

Generally, too much flow based off of what I've seen and the research would
suggest for an optimal substrate. Cables will not hurt really, but I think
they might only help in the start phase. I have zero issues I can relate to
the substrate methods I use.

But if folks want another gadget they don't really need, they can get one. I
don't buy George's or Dupla's theory about them though. If it's true, it's
very subtle at best and teasing apart the cause and effects is very dubious
at best. These types of studies can be done but are a fair amount of trouble
and have many parameters to consider. Hobbyist simply do not have the
equipment to measure and gauge this type of comparison.
Even scientist have trouble maintaining the control while manipulating this.
There's plenty of room for speculation and little for real argument.

But on a "does it work level", it's counter to my own experiences and the
observations of Tropica and other folks. There's an awful low of speculation
and results don't match the claims in any significant amount.

"Miracle Wonder Plant Juice" with PO4 would do more for a tank than cables.

But thanks for the cheaper cable alternatives from the UK. Having used 3
brands over the years and having built a few, I see little need for a cable
in the first place.

Where is George? He better come to Dallas for this year's AGA meeting!

Regards, 
Tom Barr