Hi,

I would like to get your thought on water movement in a planted tank, what you did with your tank and the result.

There are two school on water movement, fast circulation with 2x-3x tank capacity/hour and slow circulation with 1x-1.5x tank capacity/hour.

Fast circulation is thought to provide good circulation of nutrient and CO2 to the plants and remove any build up of waste material from the surface of plant leaves. This might be true in a large tank as the CO2 reactor is usually located at one corner of the tank and may not circulate well if there are pockets of stagnant water. You can see this from the direction of O2 bubbling.

Fast circulation can be achieve by using a large filter or smaller filter with an additional powerhead to circulate the water. Using large filter with too much water circulation can reduce the effectiveness of bio filteration. We can reduce this by using filter with controllable flow but this is contrary to the purpose of using large filter to create good circulation.

One method to increase water movement is the placement of filter return. Place it low near the bottom of tank will create strong current and good for plants that like strong current such as cryptocoryne but might uproot stem plants especially after pruning and replanting. Placing the return nearer to the top of the tank will create strong water movement at the top but may cause debris to accumulate on the gravel and less water movement for dwarf plants.

So, we need a strong water movement and good biological filteration. This probably can be achieve by using slow filtration with powerhead or large filter with a section of the filter blocked to slow down a portion of the water getting thru the filter similar to Dennerle's filtration system.

Okay, so what is your preference and what have you implemented in your planted tank?