Buffers in general are a very poor choice for trying to raise or lower the pH of a reef aquarium because they do not solve the problem (excess CO2) for more than a day or so, and because continued use will boost alkalinity too high. The effect they do have is largely instantaneous, then declines as the tank equilibrates CO2 with the room air.
Seachem Marine Buffer is an especially poor choice for use in a reef aquarium as an alkalinity supplement (Seachem sells it for FO, not reefs) because it has a large amount of borate in it.
Very likely, the pH will again be low tomorrow, and the alkalinity may now be creeping up if you keep on using it.
Better ways to raise pH include more aeration with fresh air, the use of limewater, or the use of a balanced two part calcium and alkalinity supplement.
This article has more:
Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm
and
The "How To" Guide to Reef Aquarium Chemistry for Beginners, Part 3: pH
http://reefkeeping.com/issues/2007-05/rhf/index.php