Just seeing this. Rapid breathing is of course a general symptom. As such, there are a number of possible causes. Linking it to a second symptom is typically required in order to make a diagnosis. In this case however, there doesn't seem to be a second symptom. Here are the causes of rapid breathing in roughly descending order of frequency:
Water quality issues (affects all fish)
Velvet/Amyloodinium (rapid death, soon affects all fish)
Flukes (slow onset, often only some fish affected)
Bacterial gill disease
Secondary to coccidia infection (no treatment)
Viruses?
So - you were correct in adding aeration and dosing with prazi.
Prazi doesn't give immediate improvement - it takes a day or so for the fish to recover from the fluke damage.
If the fish is still alive this morning, let us know and we can try to figure out next steps.....
Jay