I just discovered my redtail shark swimming listlessly in a vertical postion in my tank! all the other fish are fine at this time as was the shark earlier this morning,I have checked all the chemical levels all check just fine (since discovering the shark). whats going on? I have had the fish for about 3 weeks,untill now had acted like a normal shark! I am going to do a partial water change in the mean time, by the way my last change was 2 days ago with a 30% change. Any help or insight will be appreciated!