Pachira Aquatica - leaves dropping and my grow-lamp

Hello,
This is a question regarding my Pachira Aquatica tree - see the following pic : http://tinyurl.com/ycohjd4 . I got it back in June, and it's been shedding leaves ever since. In the summer months it's wasn't too bad after it stabilized, but then in the recent months it's been loosing a branch of 6 leaves a week - sometimes 2 per week.
Sadly it's becoming a former glory of itself, which is shame cause it's a really cool talking point in my flat, and I love it. So much so that I thought some additional light might help. Remembering my friend's from university 'grow up', I bought a sodium floodlight which is on from 4am to 7am, and then 9am through to 6pm.
I did some cursory research after wards and read that halide lights are better than sodium lights as plants have a better reaction - I was always taught that orange was the best colour because it was absorbed most by green leaves. However it seems that the colour temperature has a bearing on the efficiency of the photosynthesis...
My flood light's about 75W - is that strong enough, or is it not going to make any difference? Would a 150W halide bulb work better? Since I installed the lamp about 3 weeks ago, I've not noticed any reduction in the rate of drop-off.
I think I'm sadly resigned to the fact that my flat is just too dark (no direct sunlight except in Summer for an hour) to support such a plant, even though they are advertised as being low light plants.
I don't think the leaf drop-off is due to over / under watering - the planter has a bed of gravel and I keep that wet to aid humidity, and I spray the plant every week or so (I travel a lot so I'm not actually here that much). I let the top of the soil dry before watering - again - typically every week. The flat's warm all year round.
Any advice?
Thanks in advance,
Tom.
--
tjrundy


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I'm no expert on grow lights, but I am over wintering, again, my stevia plants under 2', fluorescent T5 lights, and after "some" initial die back, they rebounded and are now pushing again and flourishing without any natural light. I'll soon be installing a larger 4' bank of lights and hope for even healthier plants. I think that T5s may be the cheapest way to go, unless you have already heavily invested in another approach.
Good luck,
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In article

I forgot to mention that you'll want to get the T5s in k5000 or k6000, which is the vegetative end of the spectrum. K3000 will give you blooms, which you may want if you are growing an "alternative" crop.
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