You need 1.25 kg of gas. Candles don't consist solely of oxygen, the ones the Russians use utilize lithium perchlorate (LiClO4). When they finish burning, you are left with a lithium chloride ash (LiCl), which will be 40% mass of what you started with.

It works out to be more efficient, at least in terms of mass, to send up large tanks of compressed gas instead.