I am in the final stages of preparing a tank for an octopus. I am a bit concerned about the gas exchange, considering the lid on the tank, and the refugium is contained in the tank stand. I ordered a Tetra O2 test, but it wasn't very helpful. Very small variations of pink in the test sample are used to indicate significant variations of dissolved O2 (increments of 3 mg/l). I checked with my wife to get a second opinion on my reading, but her interpretation was a reading that would have been well over the saturation level for my temp/salinity. I guess, all I really know from this test is that there is some level of O2 in my system. Has anyone had experience with a good test kit?