Originally Posted by Pasfur
In the event that water quality is not an issue...
In my freshwater days I had a lot of experience with Tiger Barbs in various tank sizes, ranging from smaller 20 gallon systems to upwards of 125 gallons. Having considerable experience with this fish, this thread caught my attention.
I think the problem you are describing in inevitable in a 20 gallon tank. Even if you are not seeing aggressive behavior, the fish sense the aggression. The weakest member of the shoal is isolated, and slowly withers away and dies. This almost always occurs in these smaller systems.
Success with Tiger Barbs really required a 55 gallon tank or larger, and either a larger school or a nice dither fish to attract the attention of the more aggressive members of the group.
I agree with Pasfur.
In the wild, these fish school in the hundreds if not thousands and even in these large shools, the weaker fish, smaller fish,are subjected to pecking order which will leave them isolated from the larger school. The minimum number suggested for aquariums is exactly that. These fish, like most schooling fish,, in my view should be kept in groups of a dozen or more. This means larger tank for many folks .