Personally I feel Co2 is part of it, but is it the biggest part of keeping BBA and other algae away? Why is the water change so essential to keeping things pristine? Pretty simple to me your diluting any nitro organic decay, but at the same time your creating fluxing co2 levels are you not? If you increase water changes to every day are you going to get more algae because of the constant co2 flux. I don't think so.