Re: Aquatic Plants Digest V1 #292

From: Bob_Hoesch at mail_fws.gov
Date: Thu, 29 Feb 96 08:24:13 MST
Subject: Heating Pad v.s. Substrate Heating Cables

I wrote:
 >What are the reaons for using heating wires in the substrate versus a
 >heating pad under the tank?

Bob Hoesch replied:

> Though I'm not aware that this has been tested in any systematic
> way, the hypothesis is that the heating coils inside the tank set
> up alternating areas of heated substrate and unheated substrate.
> This is supposed to set up cyclical convection currents which bring
> fresh water and dissolved materials down to where the roots are.
> Consensus seems to be that a heating pad underneath would warm the
> substrate uniformly. Consensus also seems to be that this would be
> a "good thing" but would not lead to the water/nutrient turnover
> that is the key beneficial process with coils. A comparison project
> would be most welcome to many folks on this list, who have argued
> over this for at least a couple of years.

This calls into question a lot of the theories on substrates, such as the
debate on the benefit of anerobic substrates, the desire to keep nutrients
in the substrate out of the water where they will be used by algae, versus
the aforementioned "water/nutrient turnover". A comparison project would be
a good idea!

I wonder what the circulation patterns are like with a pad, after all puffy
clouds form from thermals generated over uniform terrain. Any fluid
mechanics people out there?