So its just been the one day that the Chromis didn't eat? I would just keep an eye on him. Chromis can be quite shy, they do better in groups of 3 or more. It's always possible that he's sick, though so keep me eye on him.
Your pH is fine. From what I've read, a steady pH is more important than a specific number. That being said, I wouldn't let it go below 8.0.
And just BTW, I love my cleaner shrimp!!!! They have so much personality and are always out. Mine even cleans the inside of my blenny's mouth!! LOL. He'll sit there with his big mouth open and let the shrimp clean. Haha The fish will periodically stop by the shrimp for a cleaning. If you hold still when you put your hand in the tank, he'll even clean your cuticles and hand!! My son had a small cut on his hand once and was putting the algae clip in the tank and the cleaner shrimp ran over there SO fast and jumped on his hand and started picking dead skin from the cut!!! It startled my son, but he said it didn't hurt. Love that shrimp!!!