Aggressive discus behavior when chasing other fish

[Lioness]

I've got 7 discus in a 350 litre tank, all roughly the same size - about 5 inches, and I got them all at the same time. Lately, the smallest one - and I mean only slightly smaller - is getting absolutely hammered by the other 6. I'm not talking about just one bully, it's a full-on gang-up. I understand that sometimes you get one aggressive fish, but this is weird. Is there something wrong with this little guy that's causing the others to pick on it?

[Bisco]

Not knowing the specifics, it seems like that discus has become the lowest rung on the social ladder. The constant harassment and competition for food will likely take a toll on it. Discus behavior can be quite challenging to manage. Adding more decorations and complexity to the tank might help alleviate the situation, but it's not a guaranteed solution.

[coltin]

To better understand the situation, it would be helpful to see a video of the behavior in question. If you could upload a video to YouTube and share the link here, that would be great. When filming with a mobile phone, please hold it horizontally to get the best footage.

Additionally, a photo of the entire tank would be beneficial, allowing us to see the layout and how the fish are interacting with their environment.

Considering the age and size of the discus, it's possible they're reaching sexual maturity, which could be contributing to the territorial behavior. If the smallest fish is a male being targeted by larger males, separating the fish may be the only long-term solution.

[Bisco]

Separating the fish might seem like a viable solution, but the reality is, a lone discus often struggles to thrive on its own. What's more, the next fish down the pecking order usually becomes the new target, perpetuating the cycle of aggression. A hierarchy will almost always establish itself. That being said, incorporating physical structures, like pieces of driftwood, can provide a much-needed refuge for lower-ranking fish. It's also worth noting that large females can be just as ruthless towards subordinate fish as males, contrary to common assumptions.

[FunFish]

I'm curious, if you were to separate the smaller discus from the rest, would the aggressive behavior still occur among the remaining six. You may need to consider swapping it out for a larger one at the LFS. As cichlids, discus are naturally aggressive and I've found that in my experience, they're best kept in pairs or singly, otherwise they tend to fight constantly.

[tetraTim]

You're gonna have to address the issue by taking it out, and possibly adding another one as suggested, or else it'll just hide and stop eating, eventually wasting away. Discus can be a real pain, I've got about 13 in my tank and it's weird how the pecking order can shift around too.