Suddenly aggressive

[WallyV]

75 gal established 7/4/24, with 2 Koi (pair) & 2 Golden Vail (sex UNK) Angelfish, 1 EBA, 4 Turquoise rainbow fish, 4 Buenos Aires Tetra, 6 Red eye tetras, 2 panda & 1 green Cory Dora’s, 1 Clown and 1 Rubber lip Pleco and 4 algae eaters. Today 12/14/24 EBA and 2 Koi Angels (pair) started to pick on 1 Golden Vail Angel hard. Temperature kept at 80 degrees. Started Colbat Brine Shrimp & Colbalt Color 2 days ago; to replace Tetra Color. Gave away a breeding pair of Angels 2 months ago. Can anyone provide any reason for the sudden aggression all of a sudden?

 

[danotaylor]

It's what cichlids do. Hierarchy is established through aggressive behavior. Not sure why today, but the reduced number of cichlids (moving the other pair of angels on) may be the root of the problem

 

[Gourami Swami]

Cichlid community tanks are a balancing act, and any adjustments can disrupt the "balance". It is rare to have a cichlid tank that achieves perfect equilibrium and has minimal aggression, the hierarchy will change over time. Removing the other angels may have reduced the number of targets, and the weakest link is now the one gold angel. EBA probably just jumping on the bandwagon and picking on whatever is lower than itself in the pecking order. Large tanks help with this, 75g is not "too small" but it's not so big that you won't have to worry about territory. My advice would be to try switching the scape up, break up the territories, and give the weak angel some more hiding spots to escape the bullies. You could also try adding some more cichlids to spread the aggression around. Breeding pairs in "community tanks" also tend to make things much more difficult, removing all females and going male- only for example may work better in long run.

 

[Alexxxxsv14]

My educated guess was that the formed pair have realized the other angelfish are a threat and they want to breed. You are better off just leaving that pair of angelfish and re homing the other 2. Angelfish are still cichlids at the end of the day and it is part of their nature to get aggressive specially while in breeding mode.