co2 for plants?

do you really need co2 tank or can ur plants indoor hydroponics grow descent buds with just natural co2 in the room.

OR will the water sugar and yeast do the trick for about 4 plants in a hut i mean can i buy the active yeast like at a wal mart im not sure what it looks like because im not really a grocery shopper but im pretty sure or hope that wal mar has it and just regular sugar i mean any sugar?

i also work at a beef plant and tey have tons of dry ice, so would that be better than the sugar yeast water technique?

How many plants? Room size? Lights?

Hard to answer the question without more info on your setup.

Bottom line though you should be able to get away without adding co2.