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[APD] Re: Substrate Heating

Bill W. writes:

>If you distribute the heat evenly then you won't get convection currents.

Correct-o-mundo.  Lower heat gradients will cause conductive heating
without currents.  Higher gradients will cause convection currents.  Even
higher gradients will cause turbulence, aka boiling.  Watch a pot of water
go from cold to boiling sometime. Put a neutral bouyancy object in the
water and watch what happens.

The problem is that a substrate is a very complex medium and there are no
convenient mechanical engineering tables to tell us what heat gradient is
"good".  So the usage of heating cables is a religious thing, i.e.,
mindless belief and pointless ritual.  I believe and have done the ritual.
 Heating coil infidels like Scott and Tom scoff.

Scott H. writes:

>If I recall correctly, a
>couple of folks have measured slight tempreature diffs very
>near and inbetween high wattage coils.

I measured a 5 degrees C differential.  A bit more than "slight", IMHO.

>If there is current,
>it could be the same water going back and forth without
>mixing in the water column -- who knows?

Warmer water would tend to rise, not go back and forth, IMHO. Or did you
mean recirculate within the substrate without bringing in water from above
the substrate?

>And if there are
>currents, it woud seem they are not strong enough to make a
>diff in plant growth

I've never claimed better plant growth. I claim long term stability. I see
no difference in plant growth.

>And if there are significant currents it could
>be as some have suggested, only if the coils cycle
>frequently and do not run constantly.

As is the case with high wattage coils, ala Dupla (RIP).

>I suggest they can't both be right but they could both be

Or they could both be right in different ways.  A warm substrate with no
currents will still speed up biological processes.

George Booth in Ft. Collins, CO (gbooth at frii dot com)
 The website for Aquatic Gardeners by Aquatic Gardeners
   http://aquaticconcepts.thekrib.com/  (mirror)

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