Generally no - but it all depends upon how heavily the tank is planted and whether there are any dead (calm) spots in there. So long as there is reasonable water movement at/along the surface, the O2 levels will be fine. Its a popular misconception that air pumps add oxygen to the water; they don't, but they create water movement (draw it up from the bottom) which results in gas exchange (CO2 out, O2 in). You can get even better gas exchange using submersible pumps, but they are comparitively expensive. If you tank has a spray bar, orient the holes to 'blow' water along the surface and it should be fine.