Okay Marsha, looks like you have hit the reset button on your pond and that is good. Are you certain the Prazipro is out of your pond at this time? I would not mix Prazipro and Api together. If you did water changes and used activated carbon that should have removed the Prazipro.
To answer your questions directly: Yes, follow the API directions exactly. I think they say to stop using carbon (by the way, change your carbon if your really want to use it in the future) and continue with aeration. If you can wait the 48 hours by all means do so. But if you have an ammonia spike, yes, do a partial water exchange and replace the removed amount of API. I am so confused about your water conditions. Some posts say ammonia or nitrite present. Is that still the case? If so, is there anything else 'dead' in your pond that would cause a perfectly cycled pond to go 'unhinged'? Look for a dead bird or something on the bottom.