Also - when they are not hiding, they are active, and mostly as a group, although there are still times where the original aggressor continues to terrorize the smallest one. Seriously - if they didn't turn dark, I might just think the hiding was a normal part of them all acclimating together. The death of the other discus may be totally unrelated and resembled a swim bladder issue caused by some sort of trauma or injury, but that has me really watching the tank to make sure it's not something more serious, due to the addition of the new fish. Any preventative maintenance or protocol I could follow would be most appreciated!
Smallest - 3.5 inches - Leopard
Aggressor - 4.5 inches - Red Tiger
New Fish - 5 inches - Pigeon Snakeskin