[bgzbgz]

Are you adding co2? Because this sounds kind of like a sump and you will probably lose alot of co2 from this. Also if you are adding co2 you dont need to worry about oxygenating the water too much because the plants turn the co2 into pure oxygen during the day and this is usually more than enough.

Also you do not really need to worry about biological filtration in a planted tank, first of all because plants and bacteria actually compete for ammonia in a tank. Second of all you will never run out of beneficial bacteria because it is everywhere in your tank in the gravel... on the plants... etc. The most useful part of a filter in a planted tank is the mechanical filtration, I like adding alot of filter floss to mine. It catches really small particles and also has alot of surface area for bacteria to colonize (not that this is necessary).