My Neon Tetras are Jerks - Aggressive and Fighting?

[B1gJ4k3]

I have 7 neon tetras (well 8 actually, but one is currently being treated for god knows what) They seem to be constantly fighting and chasing each other around. It doesn't really seem like it's one particular one either. They all seem to end up chasing each other around across the tank or chasing each other/fighting in a tight circle. I was hoping that moving them from a 10 gallon to a 20 would make things better. They were initially more chill as they acclimated, but are now back to the same behavior.

I wasn't able to catch them circling, but you can kind see what I mean here:

Anybody ever seen this before?

Edited March 15, 2021 by B1gJ4k3

[KBOzzie59]

I've seen this when adding new fish to an established school/colony.

[B1gJ4k3]

Well, that would somewhat make sense since they were purchased separately from two different stores. But, they've been together for at least a month now. I would have thought they would be used to each other at this point.

[Will Billy]

Not just neons, but a lot of schooling fish try to establish a pecking order as well. The most dominant neons comes out on top in regards to food, territory, first pick at mating etc... this behavior is most common when they create a new school, as in your case getting fish not from the same school. They are establishing a new pecking order. It will subside overtime with a few flare ups from time to time if one decides to challenge another to be on top. The flare up you are observing is usually quite rare in an established school of fish because they begin this dominance / submissive ordering system as juveniles, with only the occasional time to time challengers. It should subside overtime once they have sorta figured each other out. 

[FriendlyLoach]

My neons have been doing that for years, I cant get them to stop. At first I thought they were just making a pecking order, but I think it is just their behavior.  I think if you have more fish the less bad it is. 

[Ben_RF]

In my own experience, it seems to me since keeping them since the 90s, the larger the group of neon or cardinal tetras the more aggression is spread and mellowed out.  I personally do not like to keep them in groups of less than 12.  

[Ben_RF]

Other things that may help deter this behavior is by having a larger fish in the aquarium or additional flow.  In my own personal experience, a larger fish that is unable to eat them but shares the same section of the water column (if only partially) often, but not always, helps to have them group up.  Also the various groups I have kept over the years also tend to do similar behavior if there is an easy directional flow in the tank that they are able to swim against.  It may be a stupid idea, but I kind of always thought by having a bit of flow in the tank it helps to tire them out as they have exercised their energy. Now I don't keep the flow on all the time but put it on a timer.