3 year old bichir suddenly became aggressive

[Piopips]

I have recently adopted a 3 year old asian arowana and 3 year old ornate bichir. They have been together in the same tank since it was setup by the original owner. They normally stay in their areas in the tank but these past days, I've noticed the bichir often swims in the arowana's space and multiple time hits my arowana.
Please help on what can I do to fix this.
Arowana: 15 inches
Bichir: 14 inches

 

[kno4te]

How long has this been happening? Is it happening when the ornate is going to the surface to gulp air? I’d try and place a cave or log the or are can hide in and hope it keeps it more down than up.

 

[Piopips]

How long has this been happening? Is it happening when the ornate is going to the surface to gulp air? I’d try and place a cave or log the or are can hide in and hope it keeps it more down than up.

Yes, seems like when he goes up for air. The onkynchange i did in the tank was add a driftwood to lower the ph