Hi Divya, you'll most likely want to do a simple acid-base titration, using a standardized concentration of sulfuric acid (maybe starting in the range of 0.01 M H2SO4) and use a pH meter for the end point (can be 4.5 or down to 4.2 depending on composition of ions and expected alkalinity result. Results below 20 ppm CaCO3 usually would use an endpoint of 4.2). You can also use a dye as an indicator for pH endpoint, such as bromocresol green. You can find more information in Standard Methods for Water and Wastewater, "2320 Alkalinity". I would assume some of your carbonate would convert to bicarbonate with atmospheric CO2.

Mark Kessel thank you sir... for your response. Atmospheric carbondi oxide will not react sir, because I am growing algae in conical flask sealed with cotton plug.