The kH is about 2 degrees while the pH is around 6.8 (gotta check.. lots my
CO2 kit color chart hehe)
Given your light levels, I would really try to increase your CO2. With a KH of
2, I would aim for a pH of 6.4. Assuming you aren't using phosphate buffers,
that is.
See this page for recommended CO2 levels:
http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm
Leigh
http://www.fortunecity.com/lavender/halloween/881/