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Re: Sand (was RE: Aquatic Plants Digest V4 #823)

chinseeming at hotmail_com wrote:

> Hello Ivo:


> You mentioned that you are planning to install substrate cables.  Might I 
> inquire what cables you are thinking of using?  I too would like to use 

For now I selected the 100 Watt cable sold by m3 (I think they are made by 
Azoo). I will use this in a 120 gal tank, supplemented by a 150 Watt
submersible heater. The idea is to keep the cable always on, and let the
thermostat in the submersible heater to control the water temp. The tank
will be in a basement family room where the ambient temperature is quite
stable. If it turns out to be necessary, in the peak summer days I can
add a timer to the cable heater to cycle it off at the afternoon hours.

> cables in my upcoming new 50 gal tank (I started small with a laterite 
> based, CO2 augmented 7 gal).  However, the commercially available models all 
> seem to require compromises.
> No cables that I can find are low voltage; all are 120V.  I believe (I may 
> be wrong) that a low votage model would be safer.

(I already posted this, but here it goes again):

I kept wondering about that for a long time, until I remembered what I
did for my entire life in my native country, Brazil: there people do not
use gas-powered water heaters, they use electric shower heads (!!). Big
220 Volt multi-ampere units that hang over your head and heat the shower
water by having a big bare copper coil submersed in the water. The thing
hisses (!) while working. Pretty scary, but absolutely safe if you ground 
the metal external casing. For 40 years living there I never heard of 
anyone being killed. Very weak shocks could occasionaly happen because of
faulty grounding. I never experienced one, and don't know of anyone that 
felt any kind of shock with those things. Millions of households use them.

So what the heck, I thought, I used to turn _on_ the electricity when going 
under one of those things with my wet feet. The cable heater can be switched
_off_ when I'm going to stick my hand in the water. So this entire safety
business sudenly sounded to me as some kind of talk to lure people into
buiyng "their" special cables with expensive low-voltage power supplies.
Believe me, people that say 120 V and water don't mix, they simply don't
know what they are talking about. What about submersible heaters, 
powerhedas and submersible pumps ? Exactly the same reasoning applies...

So I complemented the cable heater installation with a grounding probe,
a GFCI outlet and a switch. Just turn it off when going to work into
the tank. In the unlike event that the cable insulation breaks, the
grounding probe will let the current pass to ground, and the GFCI will
trip. In 30 milissenconds. No current can ever go thru your body, which
presents a pretty high electrical resistance when compared with the
grounding probe. No brainer. 
> Pet Warehouse carries a grounded (three prong) model but does not appear to 
> come with a thermostat.  M3's can be fitted with a thermostat but I cannot 
> tell whether it is a 3 pronger.

As I said, I don't think a thermostat is a good idea. If the water is
warm, the cable will switch off and its purported benfits will be gone.
They must be on for most of the time. And the purpose of the cable is
not to heat the aquarium, it is to heat the substrate. Better leave the
heating job to two devices instead of one.

What is the purpose of the third prong in a cable heater ? Where it is
connected to ? It would only make sense if it where connected, that is
exposed, to the water itself, to act as a grounding probe. I wouldn't 
care for a three pronged device. Remember, most submersible heaters,
powerheads and submersible pumps do not use three pronged connectors 
either. Grounding the entire tank with a grounding probe is the safest

Hope this helps,