This work was conducted using two different open plate systems, mainly used as inoculum unit, to study the effect of culture volume, growth surface and flow rate on growth of the alga Scenedesmus sp. For inoculum preparation, laboratory growth was performed using N8 macronutrients solution with PAZ trace elements mixture. Out door production was heterotrophically achieved using a mixture of 0.3     g.l-¹ urea (46.5%), 0.05 g.l^-1 SoulPotas (mini.50.0% K₂O & 46.0% SO₃), 0.1ml.l^-1 phosphoric acid (85%) and 6mM acetic acid (5%) under continuous illumination. The first unit, of 1000 L capacity, exposed area of 8.78m², pumping power of 2.0 hp through out 45 mm polyethylene pipe system, 54-60 m³.h^-1 of follow rate and fueling valve of 63 mm was compared with the modified unit. The modification was operated based on increasing volume capacity to 2000 L, 19.0-36 m³.h^-1 of flow rate with large exposed area of 13.73 m² and higher pumping power (2.5 hp) through 63 mm polyethylene pipe system. The out let was also modified using total width outlet instead of whole outlet of 63 mm diameter. The modifications done increased growth of alga in terms of dry weight or total chlorophyll. The increment of growth, about 33.0% of dry weight and about 25.0% of total chlorophyll, recorded the variation of growth among two units. Growth characteristics represented variable results.