i never used co2 with my dwarf baby tears, it does need really high light though. i had 3 cfl bulbs above the tank i had it in two 10w and one 15w bulb, i just used jobes plant food spikes i would cut off a little piece and stick it under the dwarf baby tears when it would start to get a bit yellow
Anyone know the par requirements for Dwarf Baby Tears? Also at what light level do you require CO2 gas supplementation vs liquid supplements like Excel?
I don't think there is any strict PAR requirement for plants; I would say as long as you have medium light and above (say 50 micromoles per square inch of PAR), with good fertilization and CO2, HC should grow fine.
Regarding your second question, I would say at medium or perhaps medium-high, CO2 becomes a much better option than Excel (economically and also for practical reasons).