The longer you bubble it (an hour isnt much time) the more change you would most likely see. If you read about these tests most of them recommend bubbling for 6-12 hours. (this is the reason I do not think opening windows in your house for an hour or so would help much)
The fact that it went up at all says you have excess CO2 in the water. (btw, a 0.3 change in pH is pretty big, IMO) If you want to see just how much you can bubble it for the entire recommended period (or you can just look it up on the graph of pH vs. Alkalinity). Why did the airstone raise it when the non-airstone didnt? My guess is, the airstone is more efficient mixing air and water and would take less time for a pH change. I think if you let it bubble outside (out of the light to prevent photosynthesis) without an airstone long enough, you would see the change in that sample too.
I bubbled for a little more than an hour on my samples, but I wasn't looking for a final pH of the sample to be where I wanted the tank to be. I was only looking for evidence that aeration with outside air made a measurable pH change (up). This would let me know that although I don't know exactly how much of a CO2 issue I have... I do have one. The graphed information told me that it was likely to be a large problem from the specifications of my tank. That was good enough for me.
-edit-
In the month I have been dealing with this same issue in my own tank here is what I have done.
Added an airstone to the DT and to the sump. Overall change in pH was too small to be sure it was doing anything.
Added another two airstones to the DT. (four total now with two large air pumps rated for 100 gal or more) Covered the tank with a glass canopy and plastic to create a small positive pressure within the cover. Idea was to maximize surface gas exchange with the fresh air being bubbled into the tank. Overall change in pH was about 0.05. Starting to think that bubbling alone may not be enough for a larger CO2 problem.
Added a line to the overflow tube "
[hr]
". This is the opening on the upside down "U" piping that was my overflow. Its purpose is to mix air into the overflow to minimize noise. Ran this line to the outside air so that air mixing with the overflow was "fresh". At this point, I had already come to the conclusion that bubbling and fresh air lines worked, but the amount that would be required to "fix" my tank made it not cost effective nor did it make all the lines out the back of the tank any cleaner and prettier looking. (starting to give it the image of a patient in Critical Care with all the lines going into the tank) I bought all the items needed to drip kalkwasser at this time also.
The next day I was showing approximately the same overall pH increase of only around 0.05. Since I was running around 7.8 to 7.9 on average before starting any of this, this was not enough for what I wanted. I had made up the kalk drip last night and started the drip in the morning. Over the next 4 hours or so I had a very noticable increase in pH and my alkalinity had dropped from 14 dKH to 10 dKH. Knowing that pH will drop with an alkalinity drop (unless CO2 is involved), yet my pH had increased with an alkalinity drop it was immediately apparant that kalkwasser was far more effective at CO2 removal than bubbling fresh air (outside hooking a Paxton Turbo fan to one of my powerheads
thats an automobile turbo for those of you that may not know).
Since then my main concern was to maximize evaporation rate so as to maximize my ability to drip Kalkwasser. To do this, I took that canopy back off, moved all the airstones into the skimmer and placed a clip on walmart fan on the tank to blow accross the water surface. Wouldn't this just mix more CO2 into the water? I thought of that too, but turns out the Kalkwasser works faster. My nightime pH low is now 8.0 since I have tweeked the drip rate. My dKH is around 10-11 on average and I used Mg, Strontium, and 2 part Ca additives to maintain these elements (kalk can deplete all 3 of these over time).
