08-30-2010, 12:52 PM
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You've been given good advice by member in the previous posts, so I'm just going to elaborate on their behaviour.
Shoaling fish live in large groups. They feel more secure, less threatened, and many species develop interactive behaviours between fish which can be fascinating to observe. They may not swim together all the time, maybe only now and then, but they know they are all there together and that eases their stress which means healthier fish. Characins (tetras belong to the family Characidae) communicate with each other quite a lot. If you have a read of the general information on "Characins" in our profiles--click on the name "characins" rather than list the species--you will learn how they do this and why. They are a highly evolved group of fish.
Before you added the plants they had no where to "hide" if threatened. Forest fish are programmed by nature to swim among sunken logs and branches, aquatic plants or under overhanging marginal vegetation, etc. They "expect" to have hiding places if they feel threatened. In a relatively bare tank, that security is missing, and they will always feel vulnerable. They do not know they are in no danger; they only know what their instinct tells them, and that is, they are in vulnerable. Providing the plants offered them the security they expected, and they will take advantage.
Once they are settled, they will adjust and be out more in the open. It is an interesting fact that fish that have adequate refuge in an aquarium will be out in the open more than if they have little refuge, simply because the places of refuge being there tells them they have hiding spots if it becomes necessary.
A word on water flow. This also has a significant impact on stress. Again, these are forest fish; most of them occur in slow-flowing streams, pools and flooded forest. There are exceptions--this info is always included in our profiles, mentioned under the fish's natural habitat so you know how to set up the aquarium for the species. In small tanks like a 10g, a sponge filter is in my view the absolute best. I use a sponge filter in all my smaller tanks (under 55g). You might want to consider that.
What you observed before you added the plants may have seemed "OK" but in actual fact the fish were probably stressed by the issues mentioned above. Now they are getting accustomed to having what they expect, and once they realize the "danger" is no longer imminent, they will be out and about.
Final comment on numbers. Tetra need to be in groups of at least six of each species. I agree with prior comments that a 10g is not sufficient "space" for 18+ fish. Removing the X-ray [which I assume is Pristella maxillaris] and the Glowlights is wise. A group of six neons, plus some bottom fish like corys, will be a nice display with the plants (good idea having live plants). A piece of bogwood will add a nice touch and provide some more "surface" for the corys that love to browse surfaces. Corydoras need to be in a group too, 5 is a nice number and with the smaller (under 2-inch) species will be OK. Or one of the dwarf species, but they are more finicky about water conditions.