I'm not seeing where you did anything to treat the ich, other than move the hippo tang from one tank to another. Ich does not kill that quickly so my bet is the fish was sick when you bought it and had multiple bouts of the illness. In reading the thread in the photo forum it sounds like you purchased several fish becaue of a sale, and that by your own admission, the fish weren't really all that healthy looking. You didn't quarantine for the recommended period of time. Each fish should be kept separately in a Q tank for 4 weeks. Fish that are having difficulty breathing will often hover near powerheads to get the oxygenated water flow over their gills. There could be several things wrong with the clown but parasites are my guess at this point. Do you have a quarantine tank that you can use for the clown? Read the FAQ's at the top of this forum regarding quarantine and hyposalinity. From looking at the pictures, the purple tang appeared to have some spots as well. At this point, don't add anything else to this system, and have those two small tanks ready to use in the event of illness. Watch closely for symptoms.
Having the clown in the bucket is not going to help. There is no filtration or water movement and the parameters will fluctuate quickly, probably killing it. Get it into a Q tank, but my sense is it is likely near death.
