If you use DIY CO2 an air pump will get rid of the CO2 as fast as you add it. Use one or the other, but not both, unless you only use the air pump when the lights are off. What size tank do you have? If it is a 55 gallon tank, you need the CO2, or at least Seachem Excel. Then, look at http://www.plantedtank.net/forums/showthread.php?t=21944 for information about what and how much to dose.