hey maccoy.. arowanas are pretty hardy fish.. so dont worry.. i'd suggest you move him back to the 55 gal.. crystal clear water.. good aeration and temp at a steady 24 deg.. aros do get spooked and stressed easily but diseases they are super resilient and heal quick.. as for your doubt bout ich or white spot.. do check the oscar and the others for possible infection.. cos i've had oscars without a heater and every single one of them got ich and died.. easiest way is to see if the fish start scraping themselves on the tank floor and little white spots all over.. back to your aro.. let him be.. leave him alone in the 55g and switch off the tank lights but room lights are ok.. dont feed for a day..btw what do you feed your aro? my aros go without food for a week and they are still cool.. sure sign on the aro being hungry is they open their mouth wide like a yawn.. i've seen all my 4 aros do that.. anyways.. hope all will be fine.. keep posting.. cheers mate..