What would cause a RBTA to expose its mesenterial filaments?

[DarkXerox]

Here is a couple photos of one of my bta's. It keeps confusing me since I've had it for the whole summer and eats the fastest out of any of my btas. It seems to do this before the lights come on and I can't figure out if it is a water quality issue or not.

Right after lights on (didn't have my good camera):



then about an hr later: