Have you changed anything in his tank lately? When was the last time you did a water change?
Don't worry too much about the scattered bubbles at the top, my tanks get that way too from time to time.
Be careful with that filter you have in the tank. I'm guessing you have an Aqueon 2.5 gallon, I have two of them along with a MiniBow and a 5 gallon. I would suggest when you get the time to change the filter to this one:
You can get it at WalMart for like $10, and the filter pads for it are only $3 for a pack of two. It has a light hum but works much better then the one that comes with that tank- it also seems give the aquarium so much more room.
The filter you have in there right now can rip the crowns off of his tail. It happened to my CT I had along with two of my Halfmoons, all of which got shredded terribly and I had to cut their tails for them to regrow.