Approximately half a day some, or all of them are swimming really fast at particular side of aquarium glass. They are always touching the glass with their head and swimming up, down, left and right, and wagging with tails at high frequency.
They also don't scratch on stones and sand, so I guess they don't have any internal parasites.
However, I searched on the Internet and found out that some people say that their fishes do this kinda thing always when they are moved in new aquarium.
But I also found out that these beautiful fishes don't do this when feeding time approaches. So I am guessing I may overfed them in the past.
Now I am feeding them with smaller amount of flake food. And they look calmer. It may be because flake foods contains a lot of vitamins and these may give them a lot of energy.
Oh, and there is still a possibility that they see their own reflection in the glass. But I think they don't.
I will report when they stop with this behaviour.
New update here. (21.4.2012)