If you start noticing redness around the gills, that's probably due to ammonia burn. See more info below.
Ammonia Burn/fish injuries:
Symptoms - This appears as redness around the gill areas. The cause is exposure to ammonia, which can happen during acclimation, quarantine, or when a fish is placed in an aquarium which has not been completely cycled. Prolonged ammonia exposure can damage a fish’s gills, liver and kidneys, usually resulting in death within a few days.
Treatment options - Malachite Green or Methylene Blue, used either in a quarantine tank or as a bath treatment. Both help heal wounds, including gill damage from ammonia poisoning. For eye and other injuries, you can also dose Epsom salt (1 tablespoon per 5 gals). Epsom salt is magnesium sulfate, making it reef safe.