Low and/or cronic pH problems are indicitive of something amiss with the set up and/or bioload in the tank. If you constantly need to add buffers to aid the pH, you should review the set up for possible causes. In most cases it will be environmental and not chemical.
Causes: Low GPH
, tank covered with solid lid and no sump, too much ambient CO2
, heavy fish load (overstocked), overfeeding, low alkalinity (rarely), newly cycled or still in the process and/or improper placement of powerheads.
Also be sure you are not guaging the overall levels if testing early in the day. Best to test midday or later. pH will typically be at it's lowest point just before the lights come on (7.8-7.9) and climb throughout the day (8.3-8.5).