Question would be . . . . .
Did you acclimate clowns from QT to main display?
Aggression is showing but although it causes stress, there is more to this. You stated you treated for brook. What did you use and how did you treat? If I read right and copper, , , , copper is for protoan parasites and brrok as indicated by tamberav would have been:
A formalin solution is mixed within a separate container with either fresh or saltwater. Start with a quick dip in the formalin at a higher concentration then performing treatment in a prolonged bath of formalin base at a lower concentration in a quarantine tank. The longer the fish are exposed to the formalin treatment the more effective it will be at eliminating this issue. 45 min bath with quick cure or 90 mins with ruby rally pro.
If a formalin solution is not available for immediate use, temporary relief can be achieved by giving the fish a FW bath or dip in water same temperature as display tank. Even though this treatment will not cure the disease, it can help to remove some of the parasites, as well as reduce the amount of mucus in the gills to assist with respiration problems.
Treatment is best done in a QT tank using either quick cure (more effective) or Ruby Rally Pro. Ruby takes a little longer and initial treatment generally takes 2-3 days to really start going to work.
With the advanced stage of this- I recommend immediate quarantine of all inhabitants and leaving display without fish for 4-6 weeks.
Then for flukes (if present) :
You can do prazi as a precaution assuming its flukes. To be safe , dose at 80% of recommended and allow it to do its thing for 8 days, do a water change and do one more 8 day dose interval
Use airstone with prazi as it does reduce both oxygen and appetite