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re: Basic heating cable ??

Michael Meyerhoff <mmeye at umr_edu> wrote:
> How is the effectiveness of heating cables changed by the substrate they're
> placed in... are they useless in a finer substrates such as potting
> soil...do they need gravel's looseness to have the flow needed to benefit
> the plants roots. 

I don't think that anyone is able to qualitatively measure the
effectiveness of heating cables because of the technical difficulties.
We can theorize about the intended purposes of the heating coils based
upon scientific evidence. There are two hypothetical functions for
heating coils:

1) to induce circulation in order to:
1a) bring dissolved nutrients from water into contact with the substrate
1b) increase oxygen circulation into the substrate
1c) circulate decomposition byproducts back into the water to be

2) to increase biochemical activity
2a) to provide nutrients to plants by accelerating natural decomposition
2b) to increase availability of iron and manganese by biochemical means

Function 1) will be reduced by fine materials in general. If the
substrate contains significant organic nutrients, the opposite of 1a)
may occur where the nutrient levels in the water are increased. 1b) is
probably good however plant roots are probably much MORE effective at
putting oxygen into the substrate. 1c) is probably improved however may
not be essential since oxygen from plant roots also performs this.

Function 2) will occur to a much higher degree with organic materials in
the substrate. This may NOT be desirable since it increases the
substrate oxygen demand. Increasing effective fertility of an organic
substrate by rotting it faster is probably unnecessary.

Summary: I would use heating coils only in the application for which
they were designed, that is in gravel substrates with laterite or a
similar clay, not potting soil.

> I've seen a friend have good success with African violet soil with a layer
> of gravel on top.   

I generally discourage people from using commercial potting soil as
substrate. Those preparations contain large amounts of peat and do not
have enough mineral components to make a good underwater substrate for a
wide variety of water plants. While many people DO use potting soils
with good success with a large number of plants, not all plants are
suited to a strongly reducing substrate. Such a substrate also tends to
lower the oxygen levels of the tank and if disturbed, tends to release
substances which can affect sensitive types of fish. OTOH, many kinds of
plants thrive using potting soil especially with mineral soil, clay
and/or sand mixtures.
Steve Pushak                          teban at powersonic_bc.anti-spam.ca 

Visit "Steve's Aquatic Page"            http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!

Aquatic Gardeners Association     -                  technical advisor