Have you been dosing two part solution or baking soda?
If your sodium bicarbonate(NaHCO3) level is too high it will depress the pH. NaHCO3 only has a pH level of 7.6, but if that's what you're dosing it will make up a large portion of your alkalinity test.
I just used "Balance" from the aquavitro line by Seachem. It works great. Look it up and read it......it raises PH only and doesn't effect calcium or alkalinity.