Need Arowana help

[Dinga67]

Hi all, I have a four year old Silver Arowana raised him on fresh fish shrimp. He has stopped eating sits on the bottom of the tank with an occasional dart to the top. This has gone on for over a week. I dont visually see anything wrong with him. Breathing looks normal. Ive tested water parameters daily they are spot on. Even had water tested at the Fish Gallery and Fish R Us both said all is good. I have a few Bichier in the tank they are fine. They never fight. Filtration is a FX6 and a SUNSUN704B SC 150 Wavemaker sand substrate it is planted.
Ive tried salt, Melafix. Any advice?