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150 watt substrate heater cables

Scott H. wrote:
"Given your last post on this subject--if you still have the mercury
thermometer, are you eager to test cables?  If you say, "yes" it might
even inspire George!  Even if it doesn't settle whether both types of
cable setups are beneficial--it might settle the convection issue."

Gosh, I've been trying to get George interested in doing some _real_ science
for a couple of years......<GGGG>.

The undergravel setup I currently have is the one from AZOO - I bought them
from Edward of Monolith Marine Monsters (m3). I've got the 200W (42') cable
plugged into the Aqualogic Temperature Controller. Its in a 130 gallon tank
(72"x18" footprint). With that length of cable, coverage is pretty complete,
with spacing generally around 2" between cables. Because I have a three
level substrate (I described how I made "walls" to hold the terraces in
place last week), the cables don't follow an even back and forth path over
the entire bottom (so I can't say right off "where" a cable would be and
where it "wouldn't" be right now).

I have the thermostat set to come on when the water column temperature falls
to 79F. With an enclosed hood containing 6x55W compact fluorescent (ballasts
are mounted remotely so they don't add their heat to the tank), at this time
of year the substrate cables just don't come on because the water temp. is
generally over 80F (right now, its 89F). Maybe in October..........

By the way, the substrate cables are the _only_ heater in the tank. I have
several Ebo Jager's sitting in the closet that I was expecting to have to
use, but the cable is more than capable of keeping my tank at 80F during the
winter, when it can get pretty cool (this _is_ Canada, after all).

"When you did your temp checks, can you say if that was comparable to a
high wattage or low wattage electric cable."

Remember, I was using a homemade tubing manifold when I did those
measurements - I would have to classify them more closely resembling a low
wattage cable as the heat differential was not as large as George Booth said
that the Dupla cables can produce.

"I will make a guess that there is a threshold energy level that makes a
a big difference--below that level, the substrate radiates and
eventually becomes evenly heated.  But at some point, there is enough
local heating differential (from a higher energy cable) to generate
convection--then the convection would tend to keep the cooler substrate

Well, in that case, even my manifold qualified - because the substrate bed
_never_ became uniformly heated - I was always able to detect a temperature
differential of around 3F directly over a tube and in the space between

"One last musing:  If convection over the roots isn't beneficial, then
why do hydoponic tomatos look so good. :-)"

Ewwwwwww! Give me sun ripened, field grown (organic please!) or give me

Don't get me wrong - I'm not saying that heating cables don't work - I just
don't how they work and I find it odd that a group which is so skeptical
about fertilizer manufacturer's claims (which can be verified by a few
simple tests) can jump up and down so energetically when reading the mantra
of a few companies who _may_ have done some experiments but who have never
shared their data with anyone else to have the tests duplicated and verified
independently. But maybe, just maybe....since their fertilizers work so
well, and I like a lot of their other equipment, maybe they are bang on the
money. At least they work for George....<g>.

Did you read what I posted last week about measured substrate temps. in the
Northern Territory of Australia? Warm bottom sediments _are_ found in some
places in nature.

James Purchase