Amonia Poisoning

Water changes. Daily, enough to keep the ammonia at less than 1 ppm. This will help ease the stress on the fish considerably. If it's already to the point of septicemia, the tang might not make it. They tend to be pretty sensitive to stressors, and the ammonia, as well as the smaller tank, will cause problems. Removing the tank to quarantine (with daily, 50-75% water changes) and treating with a broad spectrum anti-biotic might help--but this can't be done in the main tank as it will kill what beneficial bacteria are present.

How long has the tank been setup?
 
yellow tang (bubbles) has been through alot dont realy want to isolate her from tank think it will stress her out to much as she has her favourite hiding place is there anything else that can be done without taking her out
 
Just improving the water conditions within the tank. Lots of water changes, basically. There are a few chemical media that will remove the ammonia, but they will also prevent the bacteria from developing, and when they become saturated, there will be another spike.
 
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