Borax will not raise your alk much at all. That is why it is much preferred over soda ash. If you want to try and continue aerating to see if the ph will come up on its own, that is fine. Then, if it doesn't, you can always add a little Borax. (And, actually having a ph of 7.2 doesn't hurt a thing. Just keep an eye on it that it doesn't drop too low.)