12-23-2009, 09:55 PM
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Filtration in a planted tank should be minimal, in terms of water movement and surface disturbance. The plants do the major filtration and "clean" the water; the filter is only there to create a sufficient current (depending upon the type of fish this may be more or less) to move the water through the filter media so the particulate matter can be captured (the "clear" water aspect of filtration).
I've written previously in detail on why this is important, and for ease here it is copied over:
The rate of water flow through the filter has an impact on the amount of oxygen drawn into the water, and carbon dioxide (CO2) expelled from the water in what we call the gaseous exchange. Surface disturbance speeds this up, as does higher flow filtration, airstones and bubble effects and powerheads. There are two detrimental issues to this: CO2 which is extremely important for plant growth is driven out of the water faster, and oxygen is brought into the water at levels beyond what is good for the plants. Plants have more difficulty assimilating nutrients when the oxygen level increases. But the more significant aspect is the CO2.
Submerged plants have difficulty obtaining enough CO2 in nature and in the aquarium; this fact is believed by many to be the reason for the inherently slow growth and low productivity of aquatic plants over terrestrial. Further, freshwater emerged plants have been shown to be more than four times more productive that submerged plants. The reason is because CO2 diffuses so slowly in water as opposed to air, and this limits the underwater plant's uptake of CO2 because the CO2 molecules don't contact the leaves quick enough to meet the plant's needs. Aquatic plants have to use enzymes to rapidly capture the CO2. When the CO2 levels in the water become depleted, these enzymes sit idle, so to speak, but the plant still has to provide energy to them. This results in a reduction in photosynthetic efficiency and therefore growth of the plant because energy is being wasted. Thus, any thing that removes CO2 in however small an amount will be detrimental to the plant's growth.
In a natural or low-tech system, the balance between the 17 nutrients (one of which is carbon) and light has to be there; so anything that may impact however slightly can become a critical factor in less success. The one thing we cannot "control" in this type of setup is the CO2, by which I mean that it is entirely dependent upon the fish and biological processes; with light we can control it, in intensity and duration, to balance, as we can with the other macro- and micro-nutrients through fertilization. Plants will photosynthesize up to the factor in least supply. Many have planted tanks that fail because the CO2 is the limiting factor, and algae will take over because it is better able to use carbonates for carbon than most (but not all) plants. The point here is that nothing should be allowed to negatively impact the CO2 in a natural planted aquarium.
Plants produce copious amounts of oxygen during photosynthesis, much more than they and the fish consume during darkness.
The water flow is important for bringing nutrients to the leaves and roots, and keeping the leaves free of sediments. But there has to be a balance so as not to adversely affect the plants ability to assimilate nutrients including carbon from CO2.
To minimize surface disturbance I would select a good canister filter; the spraybar can be positioned beneath the surface. As explained above, oxygen is not an issue in a planted aquarium.