Co2 is not for beginners and it can kill you.... It can be more expensive than you would think. Tank, regulator,timer, ventilation fan which can run $200 for a good one.... and intake fan, are what is really required to have co2 enrichment be worth while.
You must understand all of these things for it to be worth while. If you are looking to save money or for an easier way, just vent fresh air from outside into the grow area if possible........or you could try this
........ inexpensive CO2 Kit a friend of mine made
1. You will need an empty bottle 2liter or bigger "WITH A CAP"
2. A long piece of aquarium hose long enough to reach from the cap on the bottle to over top of your plant(s).. so be sure u measure how much hose u will need from where your bottle will be sitting.
3. At least 2cups of White Sugar
4. 2 Table Spoons of Bakers Yeast
First start by making a small hole in the cap of the bottle just big enough to put one end of the aquarium hose (or medical hose if you can get it) in and seal it with any type of glue/sealant wait to dry.
Then put 2 cups of sugar into the bottle and fill it up half way with "ROOM TEMP WATER" cant stress that enough if the water is too warm or too cold the yeast will die and not produce CO2.
Add 2 Table spoons of Bakers Yeast and put the cap on the bottle and shake it a little to get the yeast to sink down to the sugar
Place the bottle in grow room and put open end of aquarium hose over your plant... Why you ask? Well most people know CO2 weighs more then O2 so when the bottle starts to bubble the CO2 travels through the hose over your plants and when it comes out the end of the hose the gas falls straight down to your plant... Provided you don't have a fan running or any other types of air circulating devices... Will also work with smaller bottles just use less sugar.
How long will it last before changing water/sugar and yeast?
Is there anyway to tell when it needs changed? or is it best just to change every 2 weeks?
or just get a demijohn
that you make wine in and run the pipe like above, and make wine at the same time, it would last allot longer, let off allot more CO2 and you end up with quite a few liters of wine.... or beer.....