Need help/comments - 8x2x2 setup (substrate heating and lighting)

["bedlam bedlam" <b3dlam at hotmail_com>]

Hi all,
I am in the process of preparing my 8x2x2 tank as a planted tank. I have 
read as much as I could from various websites (thekrib, G.Booth's etc) 
regarding setups and the various techniques people are using. Here is a list 
of materials that I have purchased so far:
1 x 8ftx2ftx2ft (still empty with stand and hood)
2 x Eheim 2026 cannister filters
2 x 40watt NEC tri-phosphors (6500K)
3 x 150watt metal halides (5200k bulbs)
1 x Dupla S 1500 CO2 kit (bottle, reducer, reactor etc)
Gravel (2-3mm) quartz based

Question 1 (Substrate heating):
From reading many articles in various sites, substrate heating is 
recommended by many people for long term growth and maintenance of a planted 
aquaria. Currently, my thoughts are to add laterite to the bottom section of 
the substrate along with some form of heating coils.
In one particular site, it was noted that in aquarias using heating coils as 
a primary heat source and using metal halides, temperature flucuations may 
occur in the substrate. During the 'day' cycle, the halides would heat the 
water, thereby switching off the coils. The coils would come back on during 
the night cycle.
a) Wouldn't this mean that the biochemical processes and water 'movement' in 
the substrate be limited to times where the plants are not photosynthesing?
b) Does anyone have experience/comments on the DuplaThermik coils? In 
Australia, DuplaThermik coil setups are significantly cheaper than that of 
DuplaFlex (even if I got a different brand transformer and temp controller) 
and the added costs of dedicated heaters. The benefit I saw with the 
DuplaThermik was that it would continuously heat the substrate and provide 
constant water movement and biochemical reactions in the substrate(abeit 
less vigorously).

Question 2 (Lighting):
The generally accepted figure for a normal planted tank is 2-4watts 
(depending on plant selection, aquarium depth etc). This figure seems to be 
only pertinent to fl?
a) What are the generally accepted figure for those using metal halides? Do 
I have enough? I am planning to keep a mixture of fast (e.g. hygros) and 
slower growing plants (e.g. anubias sp. Java ferns) in various regions of 
the tank.

If you have any thoughts or comments on any of the questions above please 
let me know!

Sorry for this long posting...

TIA,
Chang.

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