I've heard many possible reasons. "If you don't feed, If you feed 3 times a week, If you extend the water changes to once every 3-4 months, if lighting is on the low side, do a water change that'll bring out the bubbles, increase water flow in the tank."
Who knows, I've tried different methods and have never seen any real results. My supplier always seems to be right on the money w/ advise and he had said he never feeds his bubble tips but maybe once every 6-12 months. the lack of feeding is when they bubble. I'm trying that method right know. I guess I should be happy at how good my rbta is doing and how big she's gotten since I first purchased her 3 months ago.
I guy I work w/ is having trouble keeping his alive. He says the tenticals are only like a half an inch to an inch long and it won't take food.
If any one every has any luck w/ a method I'd love to know