I am in Europe now, just checked email, replied to you with lots of different questions.
Here are the answers to your questions:
This is a tenecor tank, 80"x36"x36". It's about 450gal. It used to host one 14" hbrtg and four 13" slivers. PH is 7.0. Temperature is set to 82 when new aros arrived. I removed the large aros into another tank. And I am trying to sell them .
All new four aros are kept together.
In this tank, I only keep 1 FF, 40 feeder guppies, 3 gold fish.
I didn't feed the fish for first two days.
I worry this died aro from day one. When he arrived he start swimming head dwn, tail up. After a few hours, he looked ok but still have difficulty on balance. always hiding behind the pipe. He was floating not swiming.
Then I set up a small tank with salt for emergency.
I asked my nanny watch him while I am away from the tank. Then she told me the aro started to float belly up. When I arrived, the aro is still alive. I took him out and put him into the small tank. It doesn't help much.
He died right in front of my eyes.
The other 3 aros are doing good. They are healthy and happy.
In the past we had fish arrive after shipping which swam head down, tail up; we asked Mr.Kan what to do and he said to put the fish in a separate tank and to drop water level down to a couple inches so the fish could just rest with its head on the tank bottom. After one week of this treatment the fish began to swim normally and made a full recovery. Apparently it had something to do with the swim bladder and adverse reaction to the shipping process.
I've set up a small tank with salt. But I didn't set the water level down to a couple inches. I guess he was exhausted when controlling the balance.