I woke up this morning at 7:30am to the sound of water splashing from my fish tank. I found my discus was freaking out; swimming from one end of the tank to the other, bumping itself against the glass. It likes to stay at the top of the water leaning to one side. I did a 30% water change and added two tablespoons of salt. But my discus is still freaking out. What's could be the problem that causes my discus to be freak out like this?