If that's the case your tank isn't cycled. Google "aquarium nitrogen cycle" and "aquarium areobic bacteria"I've only had him for about 2 weeks, and I didn't move the media filter with him cause I feel like her started acting this way because I started using a different media filter. The new media filter I put in was fluval clear max
That should be enough to get you started. If you have any questions while you're researching, don't hesitate to ask.
Also google "minimum tank size for arowana" and read up on that.