if you find the pivot point of the bubble try to twist evenly but gently back and fourth with that point. kinda like how a top spins i guess is the best direction comparison i have. If it breaks it will release spores (probably thousands) in your tank. if your iffy about one and dont know if its going to break or not remove the rock if you can when doing a water change and put it in the old water and scrub that bad boy off in the old water with a brush. and just so i cover my bases make sure its a brush that is specifically for your tank, nothing that you have washed dishes or put soap on or anything like that.