Yup, that is your answer. pH is always the lowest in the morning before the lights come on and the highest at the end of the day right at lights out. Just the way it works. The ideal thing to do is to get a automated doser that will slowly dose Alkalinity suppliment overnight so the pH doesn't drop as much... something I still need to do myself.. just waiting on
Bubble Magus to release their dosers in the states. Best price I have seen for one.
As for the skimmer.. ya, I am seriously contemplating building an Algae scrubber myself after reading all the positives on them, especially from Amphiprion.