ALL algae is the result of a compination of factors, Light, CO2, phosphates, Nitrates etc. As far as phosphates and nitrates they can exist at levels too low to read from your home test kit (read previous articles of Sea Chem on line-stating 1PPB is enough to suport micro algae). Your buble algae is the result of the elements listed above and an abundance of CO2-that is what fills the buble. Your algae is not bad at all and is the result of a established tank. If it is really ragging you, then cut the hours of light and it should go away (what I mean is REDUCE the hours of light and NOT leave them off altogether). GOOD LUCK-at least you do not have hair algae. I have struggled with for so long I am working on my doctorate degree on hair algae!!!!!!!!!!!!!!