Ive heard both ways on the bubble algae popping, did a non scientific experiment, had one rock with 2 BA bubbles about the same size, put them in 2 seperate 10g tanks and poped one. The tank I poped one in had 6 more spots 3 near the poped piece and 3 a few inches away, the other tank I let just grow and it never spread....... Im not saying it always happens, nor was that little trial a perfect trial, could have been millions of variables, but regardless I try not to pop them now.