Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
One large filter or two mid sized filters will both work.
If you have 2, then you can alternate cleaning them. This way any disturbance of the nitrifying bacteria is not so much of a problem. This is lower priority in a planted tank, however, and is not enough reason for me to go with two filters.
Two filters implies two water flow patterns, each filter having an IN and an OUT. You will need to coordinate these so that they do not cancel each other out. One way I did this on a 5' long tank was to have the OUT to each filter pretty much in the back corners of the tank, and the IN from each filter about 1/3 and 2/3 of the way along the back. The filter tubing crossed behind the tank, so that filter A had the OUT at the north end and the IN on the southern 1/3 of the back wall. Filter B had the OUT at the south end and the IN on the northern 1/3 of the back wall. Both of the INlets aimed for the front wall of the tank.
I have done other 2-filter systems such as a sump and a canister or a sump and HOB.
Overall, though, I prefer one filter and a power head.
A planted tank really does not need that much filtration. Good water movement is important, and with driftwood, rocks and lots of plants there can be dead areas. So set up the filter where it seems to do best, then add a PH to correct dead spots.