after a bit of research, i found a little site with hydroponic lessons/methods/explainations whatever, and concluded this is a passive system, heres a brief quote from the site...

Passive
The advantage of a Passive hydroponic garden is its low maintenance. A Passive system does not use pumps or timers to flood the root zone. The roots usually dangle in the nutrient solution and draw what they need from it. A Passive system is generally slower growing and not as intensive as the other systems discussed.

Because there is no water movement, passive systems will often have low oxygen levels. this can be remedied by adding a small air pump that pumps air into the nutrient reservoir.
the difference is, that the water IS moving, which should solve the low oxygen problem... - i think im onto something...