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Re: Undergravel heaters

Justin Frese said: 
>      i personally do not use any sort of substrate heating.  I am not 
> clear as to the substantial benafits.  I was wondering however, Why 
> dont you do like the reptile keepers and use a cheap "Thrifty's" back
> heater?  Would this be too hot?  I mean under the glass of course and
> not submerged! 
>       Also, if you need it a little cooler, you could use
> plumbers tape (what they wrap around water pipes to keep them from
> freezing.)  You just need an inline adjuster to turn up the watage a
> bit.  This would as well, go under the glass.  My stand allows me to
> access the bottom of my 60 Gal. but perhapse not all stands do so.
>      Is this not a plausable idea?  

I believe there are two (speculated) goals of substrate heating:

(1) A warmer substrate (potentially) increases plant root metabolic 
    activity in the substrate.  New roots can grow more quickly and
    older roots are more capable of maintaining health.  Of course,
    the additional root activity can increase the potential for
    nutrient uptake.  For terrestrial systems, root growth
    limitations are a primary factor in limited plant growth
    (being the central requirement for nutrient and water uptake).
    I suppose a warmer substrate will also increase the breakdown
    of waste and accelerate its availability for the plants once
    again, as well as increase the activity of critters you may 
    have in the substrate to break this waste down (snails, worms,
    other protazoans, etc.)  (I bet most aquarists would be 
    *shocked* to find out what REALLY grows in the substrates of
    their establshed tanks.)  :^>  If you have RUGF or UGF as a 
    filtering mechanism (ammonia to nitrite to nitrate), then a 
    warmer substrate would conceiveably accelerate the bacterial 
    population growth potential and increase the buffering capability 
    of your biological filter when a big fish dies.

(2) As an ancillary goal, it appears many people are looking for
    heat in the substrate to circulate water through the substrate.
    Heat coils are capable of setting up highly localized convection
    currents, which (if distributed over the bottom of the tank)
    should provide [very slow] circulation.  The "very slow" is
    a primary goal:  we are speculating that nutrients in the
    water are better able to get "caught" on exchange sites for
    later plant root exchange if the nutrients go through the
    substrate "slowly".  The typical speed of a powerhead may force
    too much circulation that we are actually "washing" the
    nutrients from the substrate with our (relatively) nutrient
    poor water in the main water column.  (Remember washing 
    chemicals from soils back in soils class?  :^)  Similarly,
    the small heater in the air-lift tubes that a couple of
    people on this list are doing are to get "slow" circulation.

I think you are right--your ideas are plausable, and would 
definately seem to be adequate for (1).  If you are not going for
active circualation through the substrate (some people have stated
that (2) is accomplshed adequately through diffusion), then you
should have no problem.  I suppose (with some thought), plumber's
tape (in the substrate) could contribute to (2); it is smaller than 
heat coils, though, so the convection would be less localized.
Anything below the bottom of the tank (under the glass) would
inherently be far less localized, so I guess you will mostly have
the benefits of (1), not (2), depending on the thickness of your
tank bottom.

--charley                           Fort Collins, Colorado USA
charleyb at gr_hp.com	or	charley at agrostis_nrel.colostate.edu