Good info in the responses here.
As mentioned, CO2 plays a large role in pH. Which in-itself depends on multiple factors, such as:
Apartment size (big place to small apartment => higher levels of CO2 than previously experienced, especially in the winter when your windows are always closed)
Alkalinity - Alkalinity is your buffering capacity. Low alkalinity means you are susceptible to larger pH swings with just minor adjustments (Such as high CO2 levels in your apartment lowering your pH [and raising your pH when you open windows due to CO2 concentration being reduced], or adding a hydroxide [OH-] to increase your pH). Higher alkalinity will reduce the severity of these pH swings.
Do you have a refugium?
Plants uptake CO2, therefore driving your pH higher in a natural way instead of adding chemicals.
In regards to Calcium: Do not dose this until your alkalinity is stable. Keep measuring calcium and don't dose until it drops. The main reason you'd need to dose calcium is if you have lots of hard coral or coraline algae growth. They need CaCO3 to build their skeleton. If your alkalinity isn't stable, the coral isn't thriving and will have poor growth. If the coral isn't growing and you dose calcium, it will end up precipitating out of solution (now you are wasting chemicals).
Read this:
http://www.reefkeeping.com/issues/2002-04/rhf/feature/index.php
TL

R
Don't adjust pH, alkalinity, or calcium to an arbitrary target. Keep them stable and you will have a happy tank.
Read this:
http://www.reefkeeping.com/issues/2002-04/rhf/feature/index.php