It's my hippo tang. He's been scratching on rocks in the tank and has some very small white dots on him, somewhat evenly distributed. This morning, three larger (.75 cm in diameter) white splotches appeared on his side. The splotches looked like someone had marked him with white spray paint (opaque center, faded edges, etc.). The large splotches faded away by this afternoon, but the tiny white specs are still there. He is eating and swimming around just fine, but he has been spending some time (not all of his time) in the powerhead stream. I'm not sure if he's having trouble breathing, or if he just likes the current. His breath rate is normal.
His history: My tank has been recovering from an ich outbreak. All the fish have been in hyposalinity for four weeks and the main tank has been fallow for the same time period. I recently moved a few of the fish back to normal salinity and into the main tank. The blue tang looked fine under the lighting of the QT (dim lighting), but as soon as he was in the main tank I noticed the white specs. The brighter lighting made them more noticeable. He also began scratching on rocks (I'm really upset at this point, because now he's impossible to catch without dismantling the tank - AGAIN!). I then remembered that I had seen some scratching behaviour from him in the QT tank as well (while under hyposalinity conditions). I figured it was just the fish itching himself. I thought that ick was unlikely, since he had already been at hyposalinity conditions for 3 wks when I noticed the scratching. Also, this fish had never shown signs of ick during the outbreak and was simply being treated as a precaution with everyone else.
Considering that the white specs are much smaller than what I have normally seen with ick, the large splotches, and the extra time in the powerhead current, I'm inclined to think that this is more than ick. Velvet came to mind. Several months ago I purchased a naso tang that had the same large white splotches on his side. He seemed very happy for four days, then reappeared a few days later gasping on the bottom of the tank. If this fish has the same disease, I don't want use the "wait and see" approach. (Note: The naso tang episode was a long time ago, so the hippo tang never came into direct contact with the sick naso tang.)
Sorry for the long letter. Let me know what you think.
P.S. All tank parameters are normal.