05-10-2012, 08:49 AM
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Well first, all tanks, planted or not need water circulation. Water circulation is very important to prevent thermal gradients in the water. Almost all of the biology in the tank needs water circulation to deliver nutrients...and yes, water turbulence on the surface aids in the gas exchange of co2 and oxygen and your water needs oxygen to support life. You do not need a water fall, so the water level can pretty much be within a half inch of the very top or at least level with the filter lip (assuming a HOB).
Otherwise, you always want just a bit of surface turbulence to oxygenate the water and general circulation for the reasons given.
If the turbulence from the filter is too great, you can fashion a simple baffle from a water bottle (instructions in DIY here).