Vibrant is not safer, you can read about here:
I've had these lions for over 7 years, there's also another one in this tank for 8 years. I had let my 210g go and it was riddled with algae, so i clean it up and dosed Vibrant, I was amazed. After 3 weeks the tank was so clean I have to start feeding my tangs greens again. I was so impressed I...
www.reef2reef.com
I should have known better, being lions and all, some fish react more negatively to these tank cleaners.
In your situation, it is obviously to do with the dino x. The skimmer was providing the extra oxygenation needed, and when you shut it off, that's what did it. I would do series of water changes to get it out and bring the ph back to normal, If you test ph, you'll likely see a drop as well, unless it has already bounced back.