update: plants dying

Yesterday I wrote:

 > Well today i started of my CO2 injection system after noting that 
 > all
 > the leaves on my Amazon swords were developing brown spots on them.
 > It is only a simple yeast reactor now in my 29 gallon tank but it
 > should be better than nothing.
 > I also checked my initial water conditions before starting the 
 > reactor.
 >         Hardness was at 55 ppm  this seems extremly soft
 >         PH was at 7.6 or higher since that is the max on the scale i 
 >                       used
 >         For lighting i'm using 2 20 Watt GE Full Spectrum bulbs 14 
 >                       hours
Well after 24 hours of CO2 from a bottle of yeast ph has dropped to a more
reasonable 6.8 just before the lights went on for for the day.  However my
yellow and brown spots are still growing bigger. 

Should I increase the hardness to say 80 or 100 ppm?  Note 55 ppm relates
to about 3.3 grams per gallon or a bit less.  And if so how much baking
soda should I use for this?