emergency help needed

[Squid]

Did a stupid thing last night, I just got home from work and I turned on tap to add just a little bit of water into my tank.

problem is I went upstairs and forgot to come back down. wife discovered only in the morning my tank has been overflowing whole night.

I lost a BD, but noticed my arowana seem to have been hit hard
would appreciate advise from bros here.

I dosed with Seachem safe. then added some more aeration.
what else can I do? I also added a little bit of salt.

my aropwana has turned pale and seem to be gasping for air, he does swim but I am worried . hoping he pulls through.

any other think I can do?