The procedure in radioactive carbon is the same with that in dioxide production technique. However, the radioactive carbon procedure is more sensitive when productivity is very low. In this technique, paired light and dark bottles are also used. Both bottles are injected with a known amount of bicarbonate having the labeled radioactive carbon. After a certain time of incubation at the proper depth, the samples are recovered. In each sample, the phytoplankton are gathered on membrane filters and dried. The quantity of radioactive carbon take in by the phytoplankton in the bottles is then measured with a device called radioactivity counting device. The net of primary production would then be computed with the use of right conversion factor.