Alternates/addition to CO2 and lighting

Hello again,
        Two questions.
        What are the specs( lumens, spectrum, etc ) of halogen lighting? I
was wondering if it could be used as accent lighting to supplement plants
that need a little more then the florescent hood may provide. Or is there
another type of bulb that can be used as a spot light or two in a hood that
will satisfy the plants needs?  
        As a "substitute" to CO2 what about crushed coral/shells.  I don't
like relaying on the CO2 to maintain a lower pH but I also understand the
ramifications of biogenic decalcification.  My plants flourished until they
reduced the KH from 150ppm to 20ppm even with weekly 15%-20% water changes,
then they stopped growing.  Do plants assimilate the carbonates as easily as
the CO2?  
Thanks, Jeff