My royal pleco is sick?

Hi bro, i've uploaded a video showing my pleco is floated frequently.

I just change 1/2 water yesterday and put quite a number of k-leave. Not sure if it is because of the k-leave.

I've transfer the fish out to a small container and change 1/2 of the water again. Pls advise if it is the correct way to rescuing this fellow.

http://www.youtube.com/watch?v=X3mmWxoGrI8