Today I just bought a rainbow Arowana from a flea market aquarium. It is at least 10 inches and looked healthy in the store. However, upon arriving home I noticed that the arowana seemed really stressed and stiff inside the bag. I let it sit in my tank for a while with the bag open and poured a little of my tank water into it. After about 10 minutes I notice that the arowana wasn't swimming anymore but rather resting on the bottom of the plastic bag. So I decided to drop it into the tank but my power head just pushed the arowana away and it keeps on sinking to the water and then swimming sideways/upside-down. Can I save this fish?