BTAs sometimes split when they are healthy and doing well, the ocean has very large patches of clonal BTAs. At the same time, under stress they also split. If you have a nice size seemingly healthy BTA in a tank that has high water quality, then I would assume it's splitting naturally if on occasion it divides. On the other hand, if your BTA divides when conditions in the tank leave something to be desired, then I would assume a stress split.
