Local home brewing store.
There's 3 different qualities of CO2, FYI - industrial, commercial, and medical.
Industrial is kept in regular old steel cylinders and has some impurities (I believe it's 92% pure CO2) and is used for welding and other industrial processes.
Commercial is in steel alloy cylinders used in the restaurant industry and the CO2 is of better purity (95% I believe).
Medical is the best (99%) and the cylinders have an inner lining of glass to maintain the purity.
10 gallon acrylic fw planted. 6 HET rasboras, RCS, pond snails & MTS, ludwigia repens, Marimo & java moss, AC50, Finnex Planted+ 17W LED, pressurized CO2.