Don't get all too happy with your yeast activated CO2 yet. If you have a chance, go order a CO2 drop checker and to measure the actual CO2 level in your tank. The recommend level is 35ppm with the drop checker color in light or yellowish green. People with medium to high light tanks would need more than 35ppm of CO2. You may be surprised that you may not have enough CO2 level in your tank. When algae kicks in for some reason, you would realize that you can't further increase your CO2 level without adding another bottle of yeast. Often times, increasing your CO2 level is the best way to combat algae, especially with BBA. Or you can also reduce your lighting. Well, $30 for few months? It only costs me $18 to refill my 10lb CO2 tank which can last me 3 months. For some, it can last as long as 6 months if they don't inject a lot of CO2 like I do. If you look at it this way, your DIY CO2 is no longer cost effective.