Seachem makes a purple labeled product called "Reef Carbonate" which raises Alkalinity. it comes in liquid and powder form. I recommend the liquid form as a beginner and graduate to the powder later on as it is easy to overdose your tank with the powder. Follow the directions and you should be fine.
I would not worry too much about it until you are looking to add corals. If you are using premium salt (reef crystals, oceanic, kent marine) it should have high levels of calcium, Alk and other trace elements. If you use a cheaper salt, the levels will be lower. Maybe check your salt? Also, take your water to the LFS and have them test it to get a second opinion before doing anything drastic.
-Doc