IMHO, if you don't know why the pH shifted and how quickly it shifted and whether it swings, you can't prevent it from happening again or even right now.
Your water might not be buffered enough, that is having too low of KH carbonate hardness and/or you have too much waste accumulated and acidifying the water. IDK which way was the shift but the scenario I am describing is a shift to lower pH.
A shift to higher pH could be due to wrong substrate, like coral, or using too much crushed coral in the filter to increase the KH.
