what is baking soda for

A level teaspoon of baking soda will raise the alkalinity in 50 gallons by about 0.4 meq/L.

You need to make sure you have an alkalinity test kit and you should aim to keep your alkalinity between 2.5 - 4 meq/L.

PH&Alkalinity are linked. Alkalinity and Calcium are also linked. Lets just say those are very simple statements and there are alot of other things that play into it, such as CO2 levels etc...

I would recommend using a balanced additive..... kalk, calcium reactor, two part supplement, etc.... These raise your alk and calcium at the same time in the right ratios...

I would recommend reading this article if your interested in using homemade additives to save money.
I wasn't going to say anything earlier, but if you raise your alkalinity it is going to raise your PH unless you also raise the CO2 level of your tank at the same time.

"""The pH of marine aquarium water is intimately tied to the amount of carbon dioxide dissolved in the water. It is also tied to the alkalinity. In fact, if water is fully aerated (that is, it is in full equilibrium with normal air) then the pH is exactly determined by the carbonate alkalinity. The higher the alkalinity, the higher the pH""""


In the above article there are some really good graphs that show how alkalinity and ph effect each other and how CO2 also plays a part..

Just something you guys might want to read up on sometime.