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Re: cables

Why do all the websites seem to suggest that substrate heating is
expensive? I live in the UK and can buy a Rena Cor heating coil for the
aquarium, vivarium or terrarium for a less than £35 even for over 80 UK
gallons (96 US gallons).
(Price for illustration purposes from www.aquatics-online.co.uk

Well it wouldn't be the APD without a cable comment every few months:-)

Retile heat mats run 15$ here and a controller adds another 15-20$.
Stick to the bottom of your tank. Some pads are pre set to 30C etc.

If you proscribe to the Dupla notion, you will need to have a good set up
with precise height and stability cups to hold the cables in place.

I think any and every one would be extremely hard pressed to show any
significant difference, short or long term of the reptile heating pads vs
the any cable system, Dupla or otherwise.

For the cost of even a cheap cable set up or a reptile pad, I can buy
Flourite and never have to plug anything in or have cables buried in the
substrate at all and have better plant growth. You could use both cable and
Flourite I suppose but I'm quite happy without any cables. I've used cable
for over 10 years and have had 7 tanks with them. I sold them all.

Regards, Tom Barr

From what I have read of other people's experience (since I don't have any
yet), a reptile heating mat is not as good as proper cables. George Booth suggested that 6 things are required for a good substrate (see http://www.thekrib.com/Plants/Tech/heat-cable-why.html). Only two of them were caused simply by the increased temperature (although it is often beneficial). Two of the others I rely on convection currents set up in the substrate by the temperature DIFFERENCES the cable sets up.
..\/..^^..\/.. . substrate
..\/..^^..\/.. () cable
..\/..()..\/.. ^^ rising convection current
..\/..^^..\/.. \/ falling convection current
..\/>>^^<<\/.. >> sideways convection current
Note that water is absorbed from the water column and circulated water is returned to it.

The things needed in a good substrate in the words of George Booth (for the rest of this email until I say so):

1) Provide warmth in the substrate for certain plant species (Barclaya
longifolia, specifically). In this case the substrate should be warmer than the water. 2) Provide warmth in the substrate to speed up biochemical processes.
3) Transport nutrients from the water into the substrate. Important
nutrients would be ammonium (fish waste, etc), iron (from trace
element additions), calcium, potassium and other trace elements. This will replenish nutrients used by the roots and provide long
term viability (in terms of years). 4) Transport harmful products out of the substrate. Decomposition products may be harmful to plant roots. There is also conjecture
that plants give of low level toxins to keep other plants out of their territory (successful weeds have made this an art form). If these toxins build up due to poor circulation, the plant may
harm itself. 5) Provide a chelating medium that binds the divalent state of trace
elements with an organic molecule, enabling the trace element to be adsorbed by root hairs. 6) Provide a reducing rather than oxidizing environment so that trace elements are kept in their divalent state (usable by plants) or
are reduced from their oxidized trivalent state. Iron especially will rapidly oxidize in water with normal levels of oxygen.

Heating coils provide items 1 and 2 directly. The convection currents
generated by the "spot" heat source of the coils provide for 3 and 4.
Laterite in the bottom 1/3 of the substrate provides for 5. The slow
convection currents, coupled with nitrifying bacteria in the gravel will reduce the concentration of oxygen getting to the bottom layer of the gravel, providing 6. A heating pad under the tank will tend to warm the entire bottom layer
uniformally. This will provide 1 and 2 but I suspect the heat will
go through the gravel as conduction and won't generate convention currents. Thermodynamics theory says that conduction will occur up to
a certain heat threshold and then convection currents will be formed with more heat. I think the linear hot zones generated by proper spacing
of the coils along with the higher temperatures of the coils will provide this. Yes, there will be hot and cool zones for the roots
but I think the other factors outweight this. Schemes that use warm water flowing in tubes in the gravel (Bioplast,
for example) won't work, IMHO, because they can't generate enough
heat. Bioplast wraps some tubing around a heater and pipes it through
the gravel with a pump. The first foot or so of the tubing may get
hot enough (though I doubt it) but the water in the coil will cool off
rather quickly as it travels through the tube. If the tube is
insulated enough to keep the water hot, then it won't transfer any
heat to the gravel.
[Warmed water returned through RUGF] will provide for 2 and 4 and perhaps 6. It may provide for 1 if you heat the water before putting it through the RUGF. 3 is kind of hard since the water is usually filtered before going to the RUGF (to avoid injecting crud into the gravel) and trace elements probably will be oxidized in the filter (oxidizing is a bio- filter's purpose). 5 is a problem because a RUGF will probably push the laterite up and out of the gravel. Don't get me wrong, a RUGF *may* provide the 6 processes, but it would be difficult to get it set up with the right flows and even flow across the substrate and proper mechanical filtering, etc.
A coil setup is a "no-brainer" if you have the correct wattage.
UGF will provide 2, 3 and 4. 1 would be very tricky to achieve, if not impossible. Detritus pulled into the gravel can provide 5 but
6 is almost impossible unless a very slow flow is used and that would be hard to do evenly across the whole substrate.

(end of me blatantly copying George Booth)

If anybody wants cheap 220V substrate heating coils, the thing to do would for a US list member to take orders and purchase a number of cables from www.aquatics-online.co.uk or similiar (it just seems to be the cheapest in the UK that I have found) and pay and extra carriage charge, then distribute to the list members, although US->UK transformers would be needed. www.voltageconverters.com sell a 50W 110->220V for $5, although too small really and not for continuous use, and a plug adaptor should cost no more than $2 or $3, but a proper 100W continuous use transformer costs $15.99, and 200W $22.99, so I don't know if there would be any saving.