First, confirm that the pH reading you're getting is accurate (ie. second test kit, have your LFS or a fellow reefer test it, etc.). You really shouldn't be adding buffer to raise pH. You should add buffer to raise/maintain alkalinity. Proper alk levels contribute to stable pH levels, but you shouldn't add buffer to raise pH.
Try aerating a sample of your tank water. If the pH of the sample goes up your problem is poor gas exchange. The solution would then be to increase gas exchange. Good circulation, good surface agitation, using a protein skimmer and having a well ventilated hood/top will all help with ensuring good gas exchange.
If the problem turns out to be elevated CO2 levels in your home then venting your skimmer air intake to the outside of the house (if you're using a skimmer) or dosing with kalkwasser (which consumes CO2 in the water thereby raising pH levels) would be some possible solutions.
HTH
