So i noticed one of my yellow tangs is hiding in between rocks and doesn't come out like it use to. No visible damage but one of my tangs has a tear in a fin. The two yellow and purple that are most active look like the have hlle but not getting worse since i removed the carbon. I feed 2 or 3 times a day and water changes every 2 or 3 weeks. Had a small spike in amonia when a few crabs and snails died but went back to zero the next day. All tangs where introduced at the same time and don't show any aggression that i noticed. Should i be concerned?