small 2.5gallon planted with co2?

[splatt3]

hi, guys!
i just started doing this planted aquarium thing and i'm so new at it. i've been doing my research and read a lot of really good info to get my plants started.
anyways, i have this 2.5 gallon glass tank that was just laying around my crib. i got bored one day and placed some black gravel in it and some little rocks. in addition, dwarf hairgrass (that i spread all over the place), riccia fluitians (i placed it in this mesh netting and letting it grow out), and 2 baby (<.5") java ferns from my 10 gallon tank. i have 1 fancy guppy in it. my light is 5100k 10watt screw bulb that i bought in petsmart. i hope that is enough light for the plants (about 4 wpg). my real question is it worth injecting that little tank with co2? or should i use flourish and flourish excel?
i've been shopping around for co2 systems and wow they are not cheap! so i went on to looking at diy co2 system with the soda bottle. My real worry is the problem about my pH dropping cuz of co2.
anyone have some suggestion/s for this tiny little tank? i would greatly appreciate any suggestions. thanks! :)

[fballguy]

Flourish excel would work fine for supplying CO2. Or you could set up a DIY CO2 with a 1 liter bottle and just use half the sugar and yeast that you would for a 2 liter bottle.

[Mgamer20o0]

i would just use Flourish excel like fballguy said.

[splatt3]

i think that would be a much better and safer way to feed my plants instead of the diy co2 cuz i dont' want to risk the pH fluctuation. thanks for the suggestions guys.
just one more question though....do you guys know a place that sells Subwassetang? i really like this little plant and it is hard to find one in the states.