Carbon dioxide easily dissolves in water, creating carbonic acid: H2O + CO2 <===> H2CO3. This will soon reverse the effect of aeration, relowering the pH. So it's best to wait until the water pH is stabilized in the particular environment. After the mixture is ready, test the pH and let it sit for ten minutes. If it stays the same, there is no necessary action. If it drops, wait another 10-15 minutes, and test again. Repeat until the mixture has stabilized. If the mixture has dropped in pH to a level below where you need it for highest efficiency, you should treat it with a soluble alkali.
Most mixtures are not this sensitive; nutrient solutions are usually stabilized before being sold, to keep that from happening, so that you don't have to worry about it. Another thing to realize is that the pH will vary depending on how compacted and wet the soil is. The more loose and the drier the soil, the higher the natural H2O pH will be.
So, basically, water aeration isn't as stable, so raising the pH with an alkali will work better. I rarely have trouble with nutrient solution inefficacy from a low pH, under normal conditions. I wouldn't worry about it, unless you are actually seeing problems coming up with this. Another thing you can do is treat the soil, rather than the solution, because the soil will affect the mixture greatly when it's applied. Alter the pH only if necessary, to fit with the needs of the plants growing therein. The nutrient solution for the plants you are fertilizing should be compatible with the pH of the soil the plants are adapted to.