It all depends. How long have you had it? Usually it cycles, at night they usually look bubble tip(after pooping) during the day they reach out to the light. Make sure you have enough lighting, if its not moving around the tank there is nothing to worry about.
Mine actually look more stringy after they flush themselves until they absorb more water. During the day they pretty much stayed bubbled unless they catch some food. A lot of bubble tips won't actually have bubble tips. No one actually knows why some have bubble tips and some are long. The closest explanation I have heard was that intensity of lighting may have something to do with it. Being bubble tipped or straighter does not make one healthier than the other. I will tell you my three were straight until I put LEDs (had t5 and MH's) over the tank and now they all bubble.
I wouldn't be able to speculate on other lighting but mine stay bubbled and I have led... maybe thats really the only factor based on what we all notice?
I wouldn't be able to speculate on other lighting but mine stay bubbled and I have led... maybe thats really the only factor based on what we all notice?