A good aquarists asks, "Why is my pH low?", not "How do I raise my pH?" What I mean is, don't treat the symptoms, treat the problem. Figure out why your pH isn't where it needs to be. You can start with your alkalinity and calcium. What are they? Do not use marine buffer, all that marine buffer does is rapidly increase your alkalinity which causes a temporarily higher pH. When the pH goes back to normal, it happens rapidly causing a pH swing and harming your livestock. My guess is that the salt you are using isn't good enough and that you should switch salt brands and do a series of water changes or a complete water change. But don't take my word for it, wait and see some more responses.