There is a benefit to running the airstone at night, with CO2 off, to provide surface current which will dissipate the now unneeded CO2 more rapidly. The fish get their oxygen from oxygen dissolved at the water surface, as well as the oxygen given off by the plants as they grow. Pearling on plants is oxygen being given off with the water saturated with oxygen. With the lighting and DIY CO2 that you have, you may not reach saturation with oxygen, but you should still have plenty for the fish.
Incidentally, I have a 29 gallon tank too, and, yes, it is too small. But, when I had a 125 gallon tank, it was too small too.