Are the bubbles coming down from the filter 'waterfall' what oxygenates the water? Because if I put my water level in my tank all the way up, there are no more bubbles. I thought they needed the bubbles, so I put the water level down 1 inch so that the bubbles would start again. Do they need the bubb;es from the filter? Having the water level 1 inch down looks more ugly than having it all the way up.