It was a while ago and probably in AA. A quick search only found tests on TOC and vodka dosing.
As memory serves, the test compared a few tanks with and without skimmers running using PH, not DO and the lights on/off over time. While they are not measuring DO directly, in this test the relationship of PH and DO is pretty strong especially since they did the test comparing multiple tanks of different sizes and shapes, canopies/no canopies, sumpless/with sump. Defiantly not perfect.
The data showed that a tank that was short and fat had less of a PH swing then a tall skinny one. A tank with a sump/overflow had a smaller PH swing then a tank without. And that a tank with a skimmer had a smaller PH swing then one without, but compared to the other two differences the skimmer was statistically insignificant. I don't remember if it was a crap skimmer.
I would put the variables on skimmers impact based on type and size as performance varies a lot there plus stand construction. A skimmer is a stand with very little ventilation could easily reach a state where the O2 concentration inside the stand is lower or equal to that of the water. Recirculating 'stale' air through your water isn't going to help much compared to providing fresh air at water surface/overflow.
Maybe Gresham can find it. I would like to read it again. My only personal experience with this was with a frag tank. Had some PH issues on a tank. I swapped out the HOB skimmer for a much larger HOB skimmer I had and didn't get the impact I needed. Removed the canopy, problem solved. The skimmer helped, but removing the canopy was a better solution. Wish I had a DO meter.
On another note, been seeing a trend with people who do have a DO meter choosing to bringing back the Bio-Balls. With the ATS coming back as well, maybe we had it right 15 years ago!! hehe.
