@BII has it entirely correct!
Co2 levels will be low and short lived with soda water. If you're wanting to speed up flowering a bit, the best thing you can do is give it more light for more hours per day. Maybe start doing hydro or soilless if you're not already. A co2 enrichment setup is not needed at all until you can provide enough light for the plant to use it, as in at least a 1000 watt bulb, plus you'll want everything else dialed in and be prepared to feed like crazy! When you are supplimenting with co2, in order for it to be at all effective, the grow area needs to be COMPLETELY sealed with no ventilation to the outside, otherwise the levels will never build up enough (at least not without many, many expensive tanks or generators). After its sealed, this will add the need for more equipment in addition to the co2 stuff, like dehumidifiers and ac units to keep it under 90 to 95 degrees. Co2 is usually the last thing to add once you're already optimal everywhere else. Even in the best circumstances co2 doesn't speed up flowering so much as make them get bigger in the same time frame.
I think your best bet is to optimize your lighting in some way. Maybe a small t5 panel for side lighting?