I've always found small blue chromis to be really delicate. I can't say for sure whats going on with this one, but it is pale, breathing a bit fast, and seems to be swimming a bit unsteadily. Some background information will help us try to diagnose things, here is a link:
Aquarium Fish Disease Problem Solving Determining the best course of action for a problem with your aquarium can be a difficult task. Even advanced aquarists will often need to seek the help of others for complicated or unique issues. Our intent here on Reef 2 Reef is to offer expert advice...
You’ll find a lot of people here with the same experience with chromis. Hit and miss for me too. They are not a hearty fish. My kids wanted 3 of them. Named them maya, naya, and aya. Aya died so we had aya 2. After she left is Then it was replaced by aya 3. Long story short we’re happy now with our 2 chromis.