Royal blue tang swimming erratically

[smopinfo1]

I have a 75 gallon reef tank. It was given to me about a year ago. I have had no problems with it what so ever until recently. A have alarge tang and it seem to be swimming erratically. It has not done this in the past. It swimms in the corner and shakes for a little while, and then acts normal. Any help or suggestions would be great.

[showfish]

Need more info, to make any diagnosis. Water parameters?, is he feeding? Any dis-coloration?

[smopinfo1]

The fish is eating fine and all the water tests fine, Ammonia, Nitrate etc...

This just started two days ago so I was hoping someone might have an early diagnosis for me. There are no visual problems at all just the weird swimming. Darting, shaking, and hanging out in one corner but only for a few seconds.

[smopinfo1]

My Tang is also swimming backwards slowly, but it moves and shakes its body while it does it. Sometimes it swims backwards and up. It doesn't seem to be rubbing on anything. When the light is on it hangs out in one corner and acts this way. When the light is off it just hangs out under some rocks like it has for the year that I have had it.

[BubbaWPB]

I cleaned all the grunge off the back of my tank a few months ago, and my purple tang found his reflection... he acted real stoopid and was swimming backwards batting at that other fish in his tank with his tail spine. I hope both of your tangs do ok...