As a few said there is the natural process for which none of us really understand why the split and their is the man made intervention that changes are brings a razor out. Someone said it already there are two different opinions or views on this with mine personally being in the let Mother Nature handle it. I personally don't want a giant BTA coming up to me and slicing me in half let alone taking my left leg or right arm. Drastic I know, maybe too much drama, but you sort of get the idea.
Having owned them and seeing some fellow hobbyists having similar issues as I do, they can, in fact, over run your tank. My personal belief is that a healthy BTA will split on its own because that is how they spread, grow, self propagate, and survive. Much like a tree or plant with seeds or roots.
We started with one RBTA and it grew pretty large in our 29 gallon bio cube. About a year later we noticed a second. Then a third a few months later. Moved some into another 29 gallon bio cube and the original did it again. Tired of managing two tanks and consolidated them into a 40 breeder. Few months go by and we have 5, then 6, then 7, and it doesn't stop. Corals are fine. Fish are fine. Rock is fine. Tank is fine. BTA's just keep splitting. We give a few away and plan an upgrade. While this is going on I see some other posts with large tanks being over run by them much like Xenia will over run a tank. Some say food, some say stress, some say no idea. I agree with no idea.
Enter my 210 upgrade. I moved over the 40 breeder and right away noticed 2 more. One I know was my fault with me setting a rock on one BTA that I didn't see. The 2nd we have no idea. Maybe miscount on our side or it just split due to the tank move. Difficult to say. At this time we peaked at 20 BTA's. Over the course of about 2 months we gave a few away and 3 died for unknown reasons. Even though it was a tank upgrade, fully cycled with new rocks, and waiting an additional 3 months merging the tanks did something because we never lost BTA's before and we also lost 3 large hammer colonies.
My point in this is that if one provides a solid foundation they will thrive all on their own. It may take a few months, or even a year, but they will do their thing. Provide the environment. Provide some food (smaller is better and stay away from silversides (bones)). Enjoy the ride because they are rather, well, interesting animals.
