The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
Flashing. It could be a number of things. First thing I would do is test the water for nitrites and ammonia. If I have an ammonia spike for any reason, I will start to see some flashing. It irritates their gills.
If that's ok, I would watch the fish closely for ich--tiny salt-grain appearing white spots.
Could also be some other parasite irritating them like gill flukes.