Convection currents [et al]

> From: Stephen.Pushak at hcsd_hac.com (Stephen Pushak)
> So Kevin is right.
> So George is right.
> take a sip of your favourite beverage

Nice discourse, Stephen.  It's nice to know that there is a scientific
explanation of why we're confused :-).

> However, you could put a kind of UG filter plate under the gravel (to
> equalize the pressure on the top and bottom) and measure the flow rate
> through a tube to fairly accurately measure substrate flows produced
> by heating coils in the gravel.

My mental model of the substrate circulation (very simplified) is that
the water in the vicinity of the coils will rise and cooler, nutrient
laden tank water will come down between the coils.  With an UGF plate
underneath, I guess water would take the path of least resistance and
cooler water would come down the tube instaed of "fighting" through
the gravel?  

I might even try this experiment.  I've got a spare 29g in the garage
with UGF plates, a spare 5 amp transformer and I'm sure I can find
some wire somewhere.

Any suggestions on a series of steps?  UGF plate with no gravel first?
Different heat densities?  Karen Randall has done some work with small
heaters in the uplift tubes to get a slow flow.  Any way of
visualizing this flow with injectable dye or something?