Have you tried giving it a fresh water bath? Put some fresh water with some conditioner into a bucket. Adjust the temp of the water as close to the temp of your tank water as possible. Place the tang in the fresh water for approx. 1 to 1 1/2 minutes. He will may start to look a little weak but he should be ok. I wouldnt do this more then once a week, as it is hard on him, but it should work.....did for me, first time.