Aquaculture diversification has been set as a major policy by New Caledonia public authorities. This has been set up to carry by ADECAL Technopole which carries projects in view of developing cultivation marine species native from Caledonian waters. In this context, the development of micro-algal cultures has been identified as a priority. The study presented has been co-funded by Glencore company in New Caledonia and achieved under the program entitled Aquaculture of MIcro-algae in new-CALedonia (AMICAL) and has two objectives: (i) designing a device to bring dissolved CO2 into micro-algae cultures with a minimum release in atmosphere of this green-house gas and (ii) to assess this device by carrying out carbon budget of micro-algae cultures in microcosm. Our study has been carried out in comparison with traditional system of CO2 input by bubbling. We thus designed a laboratory scale and pilot scale simple device called “dissolved CO2 concentrator” with a capacity to produce enriched CO2 sea water (600 mg of CO2.L-1.mn-1). The carbon budget in microcosm shows a yield (CO2 retained by micro-algae/CO2 injected) of 76% when the CO2 is provided in dissolved form with our device against only 6% when the CO2 is provided by bubbling. The CO2 fixation rate by micro-algae is 13.33mg C.L-1.d-1 and 2.84 mgC.L-1.d-1 with “CO2 enriched water” and the “bubbling” respectively. Intensive culture of microalgae requires a supply of CO2. However this gas represents an important part of the production cost. Our study allowed developing a tool that could offer dramatic savings of use of CO2 in microalgae aquaculture and to minimize its impact on the environment.