Unfortunately, we never expect the worse, and spend loads of time and money to fix the unexpected surprises.
In this hobby in particular sometimes poop happens. Unfortunately, when poop does happen it happens to the most expensive / rare / precious fish. I too use prime for that reason. removes ammonia and dechlorinates. I've said this once before, and im forgetting where i sourced my info from but a by product of the removal of chlorine using carbon is ammonia.
Having said that, ammonia is less toxic at lower pH levels. but since you have baby discus I can only presume you are using more alkaline water and not acidic.