Originally Posted by Gene
Yeah i thought so to but so far they all get along besides the little fish we have the Cherry barb likes to Chase the Rosy barbs ever now and then... besides from that they get along great surprisingly and they are very active...
This is what we often hear, but I can assure you that disaster may be closer than you now think. I'll try to explain.
Fish grow their entire lives, unlike many other animals, and the internal organ development can be severely hindered if the fish, even when juvenile, is in too small an aquarium. While "space" has a part in this, the more important aspect is the water volume in terms of water quality. And I don't mean the aquarist doing a weekly water change and having a good filter; I mean the substances that are in the water inhabited by fish that can affect both that fish and other fish. As an example, discus breeders frequently raise fry in tanks that would be too small for proper and healthy development were it not for the fact that they change 90% of the tank water several times each day. This allows the fish to develop properly, with healthy immune systems and organs.
But there are other concerns too. Take the Algae eater, which I am assuming is the common Chinese Algae Eater. This fish grows to more than 6 inches, becomes very aggressive as it does, and on top of this won't eat algae except when very young. All on its own in a 30g might be fine, but not with other fish in what is too small a tank. And fish with aggressive tendencies frequently get them far worse when "crowded" young, just as fish that normally would not be aggressive, like many tetras, will turn nasty when they are on their own (as opposed to being in a group of 6+) and/or in too small a tank. The tank size, both physical limitations and the effect on the water quality, is the reason.
Most of us have learned the hard way, that the time to select the correct fish is at the very beginning with the potential size and probable behaviours taken into account. Some fish can be nasty in one tank but others of the same species seem fine in another tank; but the inherent behaviours that nature has programmed into the species are still there, perhaps latent (at the moment), but they are like the proverbial powder keg--the possibility is there, just waiting for the spark that sets it off. And too many fish with conflicting "behaviours" in too small an environment is just such a spark.
This is all meant to be constructive, for the good health of your fish.