I am having a similar problem with a tank of guppies, I have noticed them flashing a heck of a lot, in fact they are bouncing off the bottom of the tank. I treated them for white spot several times but the problem persisted. Also in the tank are otto's and b/n's neither appear to have any probs. I have moved the male guppies into a bare bottom tank which has not even been cycled and none of the fish moved appear to have any discomfort therefore I have come to the conclusion it must be the water parameters causing the problem,have not done any tests as yet.