Did you quarantine the new goldfish before releasing them to your pond?
Any new fish should be quarantined at least 2 weeks but some experts recommend a month!
And before adding new fish did you test your pond for the usual, ammonia, nitrite, nitrates and ph levels?
It's hard to say what they died from when your only symptoms are death.
I'm sorry you lost your fish, but some of those medicines are rather harsh to use on fish that you don't even know what their symptoms are. You need to determine what they are dying from before you start treating with any medications.