I've heard and read its all up to them. No rhyme or reason. I have a huge red that looked super awesome when I got him, but for months now, nothing lol. I won't buy a super expensive one because I don't want to run the risk of it not 'bubbling'.
I do bi weekly water changes, run T5s, and check my water weekly. He has moved to where he is at now, so I know he likes his position, etc etc. if someone can solve this mystery, let me know!