I went for many years without ever seeing any BBA. But, once I had my first infestation of BBA I now find it eventually in every tank I set up. Algae reproduce with spores, which, from what I read, are nearly indestructible. So, perhaps BBA once growing in our household, will be with us forever after, and all we can do is slow it down so much it is easy to get rid of when we see some of it. This should be true for all forms of algae, but BBA is notorious for the indestructibility of its spores.