An established tank CAN handle dying leaves. The problem is likely just the bba treatment, if you have to do it again, just be aware that everything that you kill in there will rot until/unless you clean it out. Even if you can't see the rotting particles, if you KNOW you killed things, do extra water changes, and/or add extra beneficial bacteria to help clean up the mess while the prime keeps it from being toxic. (prime wears off after a couple days btw, if you have a lot of ammonia in there, and not much bacterial/plant presence to pick up what gets released, you have a problem still)