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Cheap Substrate Heating

George Booth wrote:

>Think about what would be going on here.  Let's say that the water in the
>tubing did pick up some heat from the ballasts (it should since the
>ballasts typically run at 150 F or so).  So the heated water in the tube
>begins to heat up the gravel.  To heat the gravel, the water in the 
>tubing has to give up heat.  In a very short distance, the water in the 
>tubing has given up all it's heat to the gravel and becomes the same temp 
>as gravel.  Over a very long time, the gravel around the first part of 
>the tubing gets very hot and gravel downstream gets cooler and cooler.  
>This does not produce a very even heat density in the gravel.  Too hot in 
>one section, not hot enough in some sections, not hot at all in the last 

Seems to me this would be a problem with a very slow flow system 
only i.e. if the water is allowed to sit in the tubing long enough to give 
up all of its heat.  Why not increase the heat available to the system by 
cranking up the rate of flow?  Granted, the heat in the first sections 
would be higher, but you can make the difference between the 
first and final sections negligibly small with a high flow rate.

>You would probably want this to be a sealed system. Pulling aqaurium water
>in would bring detritus and clog the tube.  And dumping the water back 
>into the tank might heat the tank too much IF all the heat was not 
>transferred to the gravel.  I suspect the silicon tubing is a pretty good 

Yes, it would have to be a sealed system.  As far as the silicon tubing 
being a good insulator, maybe, but I can feel the heat off such a tube 
when I run hot water through it....Any idea on how much heat transfer is 
really necessary?

>And, of course, you would have a problem with brown algae build up unless
>you used sterlized water and somehow kept it sterilized. 

Could be a problem.  Solutions might involve adding something to the water 
in the sealed system to keep the algae down.

>How would you control the heating?  Hopefully, the on-off cycle of the
>lights would just perfectly balance the heating of the gravel so the tank
>water would not get too hot. 

Put the pump on a timer, or under thermostatic control, the same way you 
do your Dupla cables.

>And, boy, won't that be exciting when the tubing springs a leak, wets down
>the ballasts and causes a fire!  Cool. 

Seems like the risk of fire is negligible if a ground fault circuit 
interrupter is used.  Other techniques could be used as well, such as 
bolting the ballast on top of a metal plate, and fixing the coils on the 

Paul Chapman
Saskatoon, SK.