Dry ice is lame. It does work, but it's such a pain-in-the-ass. Why do you feel you need to increase co2? Just vent that stuff well and co2 will come and go.
Dude, seltzer water? You're growing a plant.
If you truely want to increase your co2 levels, buy some co2 and work it in the proper way, or vent your plants better. Don't screw around with shit like dry ice and/or seltzer water.