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Planning new tank - have a few questions...

Greetings, plant experts.

I've recently subscribed to this list and have been lurking and reading
some of the archives for a little while now.  This is my first post.  I
have kept various freshwater and marine fish on and off since I was a
little kid in the sixties, but have never kept plants.

After thinking about it for a loonnnnnng time (about 7 years!) I am
about to set up a fairly ambitious planted aquarium.  It is to be 180
gallons (approx. 72 x 24 x 24 inches).  I am having the stand custom
built and it will be about another 4 to 6 weeks before it is done, so
I've got a little bit of time to refine my plans and acquire all the
"stuff" I need.  For the most part, from the reading I've done, I think
I've got a pretty good handle on the basics, but I could use some
experienced advice in a few areas.

I plan on using wire in the substrate as my exclusive heat source, and
therein lies my first group of questions.  According to a Belden
catalog, 22 gauge stranded wire has a resistance of 17.5 ohms per 1000
feet.  According to my calculations, using 24 volts and 100 feet of this
wire will give me around 330 watts of heat.  Does this sound both
accurate and appropriate?  From the reading I've done, it seems like
people use silicone insulated wire for this, but the insulation specs in
the Belden catalog have me considering teflon.  Both materials are
excellent to outstanding in water and heat resistance, but teflon is far
more abrasion resistant.  I also suspect that the thinner teflon would
do a better job of conducting the heat from the wire to the water.  What
do you think?  I will feed the #22 wire with some #10.  I am unsure as
to whether the splices should be outside the tank just over the lip, or
at the bottom under the gravel.  If they should be inside, how would you
suggest I insulate them to attempt to prevent contact with the water? 
And finally, I intend to supply power to this cable with two large,
12-amp 24-volt transformers in parallel.  I should be putting just under
14 amps through the cable, so I believe this will be over-engineered
enough to have no worries with overheating, etc.  (12 amps is the
largest rated 24-volt transformer I have been able to find with only a
little searching.  If I can find a single, higher capacity one, I'll use

I intend to use sandblasting gravel for the substrate, with laterite
mixed in the lower portion.  According to my calculations, I'll need
about 300-350 pounds of gravel to give a substrate depth of about 3.5 -
4 inches.  It appears that the Dupla laterite may be obtainable (with
some difficulty) from some overseas sources.  Should I do this, or is
the Aquarium Pharmaceuticals "First Layer Pure Laterite" good enough? 
Any other laterite options?  In either case, how much should I use? 
(From reading the archives, I have inferred that the laterite is
unnecessary over the long term - the substrate would mature with time on
its own.  I am assuming that the laterite will not hurt and will get me
off to a better start.  Reasonable?)

For lighting, I am considering a fixture made by Hamilton with three 175
watt MH bulbs (5500K, but could be upgraded to 6500K for about $25/bulb)
and four 55 watt compact fluorescents.  Do you think that's too much
light?  Is the upgrade to the 6500K bulbs worthwhile?  An alternative
would be to stay exclusively with either compact or VHO fluorescents
(probably available up to around 600 total watts) and no MH. If I use
the combo fixture, I'm thinking I'd fire up the MH lights first (gradual
warm-up and all, plus the center MH can be controlled separately from
the other two), and then turn on the fluorescents 1.5 - 2 hours later. 
At the end of the day, I think I'd turn off the MH's about 1.5 - 2 hours
before the fluorescents, but I may play around with this idea a bit.

I'm planning to use wet-dry filtration and inject carbon dioxide via a
reactor in the sump.  Is this the best choice?  What would you suggest
for a CO2 reactor?  I saw an Aqualine (by Red Sea) on the Pet Warehouse
website for around $30 that looked sort of like a long spiral enclosed
in a tube.  It seemed like a reasonable choice.  There was also a bubble
counter of the same brand.

Well, thanks for reading this far!  I really appreciate anything you can
add.  I'm sure I'll probably have many more questions as I go along...

Looking forward to buying my first plant,
Best Regards,

Mark S. Patrick
Avon Lake, Ohio