I agree with Mike that doing a decent sized pwc
(20%-30%) will help get your levels in check. If its a newer tank then a lower PH level is fairly common and will balance out over a couple of months. Make sure the top of the tank is not covered and you have a slight surface ripple for good gas exchange as well.
Also if you checked it first thing in the morning then it's going to be lower then checking it a night just before "lights out". If you don't have a alk
test kit to measure then I wouldn't add any buffers till you do.