I'm not sure of how accurate the test kits are. I was getting a reading of 0, which in my situation was absurd. My nephew's wife works in a college lab and she brought one of their test kits and the water was saturated. The Salifert test kit gave a 0 reading. Later I purchased a Red Sea kit and got a temperature adjusted reading of saturated. If I use the Salifert kit on my pond, I get a reading that is more than double the maximum saturation level of oxygen in water. This is not a blessing or condemnation of either kit, just a discrepancy that makes me wonder. I have a 75 gallon tank with a wavemaker and at times, the movement through the tank reaches over 1,800 gph excluding skimmers. This is the wet/dry and powerheads only.
Generally if you have adequate circulation and water aggitation, you shouldn't have any concerns with oxygen levels.