I purchased 4 small (2.5 inch) black arowana last week and am having a tough time keeping them alive. The first one ended up missing it's tail and just sat on the bottom of the tank til it eventually laid sideways and died. Every now and then it would swim around and sometimes spinning in the water. Now 2 days later I've got another just hanging on the bottom and not eating. This one does not look beat up. Just swims around kinda wobbly every now and then. The other 2 and the silver of the same size with them are looking good and eating bloodworms. Tank had a small amount of ammonia present. The lightest shade of green possible. Ph is about 6.4. Temp is 84. Good aeration. No nitrites. I did a large water change tonight and put the sick one in a floating breeding box in case there was any aggression toward the weak one. Any ideas or tips? Already down one. Don't want to lose any more. The first one was clearly attacked at some point but I don't see any damage on the second one.