I have a BTA that I've had for maybe 3 years, about a year ago it split into 4, and now a few weeks ago they started bubbling almost all day on a regular basis.
Interesting. I have 2 RBTA and 10 BTA (all from one BTA). All of these are in the same tank. Both RBTA don't bubble at all and a couple BTA's bubble and the rest don't. Some of the BTA's even have half bubble half not. I always wondered what determined it but it seems random.