It lowers the KH which in turn will lower the Ph, problems only arise if you have a low KH to begin with, after a week or so in aquasoil the KH can drop to 0 and you wont get a reading for KH any more on a testkit, basically you can temporarily buffer the water slightly, to say reach KH 1, you can then make a comparision Ph/KH reading to get a starting point for adding the CO2, you dont need to continue buffering the water, you just do it in order to get a starting point for the CO2. TBH though the Ph/KH CO2 relationship is a bit screwy anyway better to just use the reading as a starting point, crank the CO2 and watch the plants for algae.
btw i dont use aquasoil but this is my understanding as to how this works, if your Ph/KH is high enough to begin with this wont be an issue, you should still be able to get a reading.
