Why do BTAs stop bubbling?
 

I've always wondered why my RBTA doesn't bubble? I've seen photos of beautiful BTAs that are bulbous and bubble up. On the rare occassion I will see some of the tentacles from my RBTA bubble but it isn't that noticeable and most of the times the tentacles are straight.

Anyone have any explanations?

There is no real 100% accurate explanation for this. I've had on more than one occasion, a bubbly BTA split and have the clone not be bubbly or vice versa - in the same tank, side by side. I've had BTAs from different collection locations as well as propagated BTAs under all sorts of water conditions and lighting, as well as well fed and half starving, and there is no rhyme nor reason nor any pattern than I can discern other than possibly that bigger BTAs may be a bit more likely to not be bubbly. That is a rather "loose" observation though.

i have personaly seen 2 cube tanks boath 90 gal that run on the same lighting there conected and almost same stock one tank aparently the btas buble up one they dont as i understand this is still a mysterie to our hobie could be rong tho