The universe wants your tank to have the same amount of o2
in it as the atmosphere around it. When the surface of your tank is calm like glass, it is much tougher for o2
to make it's way into your water. When you provide agitation at the surface, o2
makes it's way into your water much easier. I don't think you need white rapids in your tank to achieve this, especially if the current and noise that your equipment makes is causing the fish to stress and stay away from that part of the tank.
Experiment with this. Try an air stone on one end of the tank. If you have a HOB
filter, depending on what type, the cascading water into the tank may be plenty of agitation for o2
exchange. Watch your fish, they will tell you if you do not have enough o2
in the water. Rapid breathing while at rest, or gasping for air at the surface can mean not enough o2
I think you may be surprised to find out how little agitation it really takes to make everybody happy.