09-23-2009, 01:39 PM
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In a planted tank the only purpose for the filter is to gently move the water through it so the suspended particulate matter can be trapped in the pad and media. Plants do the "cleaning" of the water, the filter makes it "clear", two different things. Biological filtration in a lanted tank is pointless, because the plants grab more ammonia and nitrite than the bacteria; plus, most planted tanks tend to be slightly acidic in pH and the nitrosomonas bacteria is inhibited the lower the pH.
Canisters work best because they can have lower flow rates (some are even adjustable now) and they are quiet and easy to maintain. You are correct, there should be no surface agitation with planted aquaria as it drives off the CO2. [BTW, when you get CO2, have it on a timer so it shuts off at night; it is best not to pump more CO2 into the tank at night when the plants can't use it and it may adversely affect the fish.]
I have personal experience with Rena XP3 and Eheim canisters. Both are good filters. I have read that the Fluval is also good, but seems to be less preferred that Rena or Eheim. I have had Eheims on two tanks for 12 years, no problems, and I cannot hear a thing. The Rena was more noticeable when I first got it, but now 9after 2 months) seems to be almost as quiet as the Eheims. Both these are expensive new, so if you can find them used--and they work--go for either.
However, you mention a 36g tank; I have a 33g (3 feet long) and the filter is an internal Eheim sponge. It is just a sponge with a motor pulling the water through it. Very quiet, my only negative is that I can't adjust the flow; I have it aimed along the back wall of the tank to reduce the current. It has worked fine in this tank (planted) for years.