Okay that is not good. So it sounds like you need to medicate for sure.
As far as the buffering goes. Baking Soda is excellent, the only problem is it doesn't hold your pH up forever. But if you are doing freqent water changes you can stay ahead of it before it crashes.
Also there are many pH uppers on the market, and you should figure out a way to pre treat your water (garbage can on wheels?) It is the up and down of the pH that is almost worse then having the wrong pH. You don't want to manipulate it too much, or you will have to be constantly watching it. You can also add a substrate or coral, dolmite, aragonite to help you boost your pH.