Take this for what it is ... an attempt from a newb to help
I just re-read this thread and I don't see mentioned what you are dosing
What products are you using ?
Did you test before you started dosing ?
Again, I'll say a second opinion on the pH test would be good and if your KH is really that low, I'd go with either dc4's suggestion of using Reef Builder to get your Alk back up, or bump up your Alk dosing, until it's higher
Either way, do it over a day or 2 so you don't create anymore shock and also Calcium precipitation
This should get your pH back inline