Bro - may I know how old is ur tank? And have you fully cycle ur tank?
White patches in their bodies - most probably is due to ich. Ich may caused by stress and FYI tang is prone to have ich and this ich virus will spread to other fishes in the tank. The fish may be shocked or stress with the new environment and especially unstable water parameter (high ammonia, no2 or nitrate). The virus will be still in your tank for quite sometime.
You may enhance the pellet or mysis with a garlic guard to help improve the health of the fish and may help ich problem.
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