Reducing tang aggression with more tangs?

[Perpetual Novice]

I have a tank with a 5.5 inch desjardini, a 4 inch powder blue, and a 3 inch blue hippo. They were added at the same time and have been getting along with literally no aggression for about 6 months now. But in the last few days I have noticed the powder blue occasionally chasing the blue hippo then shaking their tails at each other before returning to swimming as normal. I’m not concerned about this yet because neither appears stressed or injured and because it is infrequent. But I know this kind of behavior can escalate. I was hoping the dominant desjardini would assert control but it doesn’t seem to be concerned by their squabbles yet.

If things do escalate my idea is to add one of two juvenile tangs from a smaller tank I also have. I want to disperse the aggression before it can become a personal issue between the two tangs. My two options are a 2.5 inch yellow tang or a 2 inch blue hippo.

I figure the blue hippo is the better option since it will outgrow the tank it is in anyway. Also because 2 blue hippos are more likely to coexist than two zebrasoma I think. But I really don’t know.

So the question is two fold. Will adding another tang help with aggression? And if so which of the options should I choose?

 

[Perpetual Novice]

I could also remove the powder blue or blue hippo if need be. I have had to catch it before when I was trying to diagnose what turned out to be a stray voltage issue in the tank. All the tangs can be caught easily since they come to the surface looking for food when I come near the tank.

 

[Halal Hotdog]

How large of a tank are these tangs in? How often and what are you feeding?

 

[Perpetual Novice]

How large of a tank are these tangs in? How often and what are you feeding?

The tank is 120 gallon. There is tons of rockwork with los of swimming avenues. Not a wall. And there is a fair amount of algae growing in the rocks for grazing. Although not so much that it is overgrown. I mainly feed the tank spiralina brine shrimp. But I also occasionally add nori and substitute mysis for the spiralina brine. I give fairly generous portions since I know that can reduce aggression. I have multiple overpowered protein skimmers to compensate for this and also do regular water changes.

I think if space were the issue I would be seeing aggression from the desjardini first. And that’s the tang which I have already made plans to rehome in the future.

 

[Halal Hotdog]

Tangs are known to be territorial, powder blues especially. Different species of tangs are known for different levels of aggression, not purely size based. 120 gallons tend to be 4' long, you might be asking for trouble housing larger species in a smaller space. The aggression may resolve or may get worse.

 

[lakai]

I wouldn't add any tangs without taking the powder blue out first then re-introducing him after a short while. My experience is that powder blues show less aggression to other fish in the tank before them but will attack anything new coming in afterwards, especially smaller. I've had luck with yellow tang and powder blue together.