Just use a 5 gallon bucket, swimming pool acid, and marble landscaping chips
5 gallon bucket - $2.89
Swimming pool acid - $8 for 2 gallons of 30% HCL; swimming pool supply shops call it Muriatic Acid (HD brand is only 14.5% and same price). Safeway (and Home Depot) sells Muriatic Acid also, but it is only 14% HCL
marble landscaping chips - 30 pounds at Home Depot for $5
CaCO3(s) + 2 HCl(aq)=> CaCl2(aq) + CO2(g) + H2O(l)
put 5 pounds of chips in the bucket and fill it with water (filling it almost to the top keeps the co2 from accumulating in the bucket top)
add a quarter liter of the acid
this will dissolve about four ounces of marble chips and generate about a cubic foot of co2 in about 8 hours; if you use a whole half liter of HCL it will produce two cubic feet of co2 and it will bubble for 12 hours (90% of co2 generated in first two hours)
the by-product of the reaction is calcium chloride (road de-icing salt)-30 pounds of marble chips will yeild MORE THAN 30 pounds of calcium salt; no harm in pouring it down the toilet just like pee
with 30 pounds of marble chips and 16 gallons of 30% Muriatic Acid ($75 total) you can generate a cubic foot of safe, clean, odorless CO2 every day for four months. Broken marble flooring tiles work too.
Don't use naturally occuring limestone - it often has minute quanties of sulphur dioxide in it. it will make your grow room smell like rotten eggs. Don't use broken concrete chunks - they are only 10% CaCO3 (but you can if you want; the problem is that you get way heavy quants of sand and gravel. If you do this, keep the sand and gravel for making potting soil)
You absolutely must have a small fan to stir up the air in the gro room or else the co2 will sink to the floor in a layer 2 or 3 mm thick.
This method works really good for increasing growth
