11-05-2009, 12:46 PM
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Just summing up and expanding a bit on the good advice from prior posts. Water current should depend upon the needs of the fish. And in a planted tank, there are some issues as well, that have to be balanced with the fish's requirements.
Fish that come from faster-flowing streams benefit from more current. I have a trio of Tatia perugiae (Spotted Woodcats) in my 115g, Amazonian fish that live in streams with a current. When I first introduced them to my former 90g tank, they took up residence in two pieces of standing driftwood at the end nearest the outflow from the filter. This didn't really click with me until I set up my present 115g tank in July and moved the plants, wood and fish from the 90g into the new tank. I moved the wood with these fish inside it, they remain in tunnels all day so it was easier than forcing them out into a net. I placed one piece (with one fish) at one end that happened to be under the outflow from the filter, and the other piece with two fish at the opposite end of the five-foot tank. Within 3 days, the two fish that were living in the wood at the opposite end moved house and took up residence in tunnels in the wood below the filter outflow, so now all three are in this wood. I realized it was because of the increased current from the filter; that's what they like.
On the other hand, someone mentioned gouramis...they should always have minimal flow in the tank. They occur in slow streams with scarcely any movement, or more often in jungle swamps and ponds with no movement. Fish from such habitats should have a quiet environment in the aquarium in order to be less stressed and more likely to exhibit natural behaviours. Most (but not all) of the common fish we maintain (excluding livebearers here) are forest fish that occur in quiet dimly-lit streams or flooded forests with little active current. It is important to know the needs of the fish when setting up a "community" aquarium, since fish with identical or similar requirements respecting water parameters, habitats and environmental factors will be healthier due to less stress.
Then we have the plants. Water movement is helpful, because it brings CO2 and other nutrients to the plant leaves faster. However, studies have shown that excessive water movement actually inhibits the plants' ability to absorb nutrients, plus the fact that it drives CO2 out of the water faster. Plants need CO2 in order to photosynthesize, and for those of us with low-tech "natural" aquaria the CO2 comes from the fish respiration and biological processes and can be in short supply. It would be counter-productive to drive it out of the water before the plants can use it.
I would never have currents that make the plants sway or even move, except those nearest the filter outflow. It is no accident that brush algae always occurs first (and most) next to the filter outflow in a stronger current. There is probably much more to this than most of us comprehend, so going with the best for the fish seems the preferred route.
Last edited by Byron; 11-05-2009 at 12:50 PM..