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Re: Undergravel heating: is it worth anything?

Steen Suder asked about the value of undergravel heating.

You can pay a lot for cables and a transformer (if using low voltage
cables). But they are rather hard to find,m espeicially if you want to
shop around for lots of different brands.

I don't think anyone disputes that cable heating can have some
benefits, mainly by promoting a very slight water current in the
substrate or by warming the roots or both.  Many folks (including the
more expert gardeneers) do fine without the cables, so the benefits
might only be appreciable if all other factors are in perfect shape. 
The benefits, such as they are, occur, if at all, only while the cables
are on or at least, on for a large percentage of each day.  Currents in
the substrate also mean that substrate ferts will be pushed into the
water column -- so your approach to fert placement might need to be
adjusted accordingly.

They can be more energy efficient than tube heaters, which place the
heat (initially) higher in the water column than heated substrate does.

If you have other significant heat sources, primarily lighting and to a
lesser extent, water pumps, tehn your tanks might not be able to
withstand more heat during certain times of the day or year or both. 
This is less likely to be an issue if you are keeping a high heat tank,
such as for discus. If the cables are off, they don't provide any
benefits.  If the they go off for a long time, then back on, they might
send some chemicals that have built up in the substrate into the water
column -- although, in a well planted tank, the plants ought to be
moving a lot of material in and out of hte substrate so there might not
be a significant build up.  Because of the "too much heat" issue, I
have turned my cables off -- they only ran about 12 hours per day for
most months of the year and not all for about 5 months per year.

In the year and a half that I had cables on the my 150 gallon tank, I
never discerned a specific benefit/detriment when the cables were on
for long periods of when they were off -- I concluded that other
factors have much greater impacts and, thus, would give me more buck
bang.  But then, I'm no George Booth (nor Karla Booth) ;-)

Hope that is some help,
Scott H.

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