The difficulties in the designing, construction and maintenance of an apparatus which will maintain sea water at a constant temperature and pH are discussed. Provision was made for carefully metered additions of inorganic and organic nutrients. Populations of particles were counted with the Coulter Counter but considerable difficulty in precise counting was incountered for several reasons 1 Debris in raw sea water was counted along with organisms, 2 Many marine forms attached to debris resulted in high counts of larger sized particles which actually represented a large number of much smaller organisms. 3 Noise in the Counter was bad in the 0.5 microns range, and, 4 Sessile organisms in the vessel and on the orifice of the counter complicated long experiments. A number of ancillary studies have been initiated to alleviate these problems. The problem of sessile organisms was partially solved by coating all surfaces exposed to sea water with several fluorocarbon coatings.