09-05-2010, 12:05 PM
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Your experience proves what I frequently write, that most forest fish do not like strong water movement. This is why in our profiles on each species under their habitat it mentions the type of water they are found in.
Filtration in the aquarium must be suited to the fish's needs, with respect to water flow. Fish that prefer still water (such as those you mention) will be stressed having to constantly battle a current. It's like you walking up a steep hill instead of on flat ground; and having to do it constantly. It will wear you out, as it wears out the fish.
Fish will naturally swim against a current because (a) they have no choice, if they swim opposite the current carries them away, and (b) their instinct says food is more likely to come at them in a current. But they need to be able to get out of it.
I have a 5-foot 115g aquarium set up as an Amazonian riverscape; the filter outflow is at one end, creating some movement, which quickly dissipates down the tank. There are fish that prefer some water flow, and they have taken up residence in wood or under wood at the end below the filter outflow. Those fish that do not prefer movement scarcely ever venture to that end of the tank; these include shoals of rummynose, cardinal tetra, hatchetfish, pencilfish, and some other characins and certain Corydoras.
One of the most important aspects of a successful community aquarium is having the proper water flow for the fish, and in a smaller tank the fish have to have the same requirement or someone will not be happy.