Need help with Bichir

[Az89]

I have a bichir that I have had for a little over a month now hes in a 40 gallon tank. He was doing fine up until this last week i noticed he hasnt been swimming around alot an usually when i feed the other fish he swims up to the top to eat an this week he hasnt. Some days he will stay in the same spot for a long time an sometimes his breathing is kinda of heavy an sometimrs its normal. Im just getting worried, I tested the wAter an everything was good except nitrites were barely showing up about .5ppm an nitrates to but i got the nitrites to 0 an the nitrates almost gone but i know nitrates arent that toxic. If someone can help or tell me if im doin somethin wrong i would appreciate it. Thanks

 

[Carefree_Dude]

how are the oxygen levels in your tank?

 

[Spiritofthesoul]

Tankmates?

I wont be too worry about oxygen level in the tank since they are able to gulp air from the surface.